I.
What is required of the ordinary Muslim is to seek fatwas and follow the scholars. The evidence for that is the verse in which Allah, may He be Exalted, says: {So [O people] ask those who have knowledge, if you do not know} [An-Nahl 16:43].
The one who should ask is the one who does not know, because the issue has to do with lack of knowledge.
Allah, may He be Exalted, says: {When they hear any news, whether it is of a reassuring or disquieting nature, they make it known to all and sundry, whereas if they referred it to the Messenger and those in authority among them, those who sought news could learn it from them} [An-Nisa’ 4:83].
Further evidence for that is the consensus of the Sahabah, for they used to give fatwas to the ordinary people, and they did not instruct them to strive in seeking knowledge until they reached the level of one who can work out rulings directly from the religious texts. That is well known and established, and it was mass-transmitted from the scholars of that era and ordinary people.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: For ordinary Muslims who do not have knowledge, their striving for knowledge is seeking knowledge from scholars, asking questions and seeking fatwas, according to their ability.
End quote from Jami` ar-Rasa’il, 2/318.
The ordinary Muslim should not seek a fatwa except from one who is known to have sufficient knowledge and to be of good character.
If he realises that a particular person lacks either of these two qualities, he should not follow him, according to scholarly consensus, because it is not permissible to follow one whose level of knowledge is not known, or to accept his fatwa, because we cannot be certain that the one who is asked is not the same as the one who asked, in terms of being uneducated (in Islamic knowledge), which means his view cannot be accepted, and – in fact – he may be even more ignorant than the one who is asking. This possibility is strong, because the assumption is that he does not have knowledge, because in most cases, Quran teachers are just ordinary people. Therefore it is essential to ask about him, and if he is a man of knowledge, he should follow him, otherwise he should not.
II.
The scholars have mentioned the conditions for the one who is qualified to issue fatwas, because it is a lofty position that is to be taken seriously, and it is like speaking on behalf of the Lord of the Worlds; not everyone can take up such a position.
Because of the difficulty of meeting all these conditions nowadays, the level at which many muftis nowadays are is that they have experience in working out fatwas and they are trained in that, meaning that they are able to work out fatwas on the basis of analogy for novel issues that are not mentioned in the classical books of the madhhab, by comparing them to similar issues that are discussed in the classical books... Otherwise it would not be permissible to accept their fatwas.
In spite of that, they are not really engaging in real ijtihad [working out rulings on the basis of the religious texts], and the one who follows their fatwa is effectively following the imam of their madhhab. All they are doing is explaining that the novel issue under discussion is something to which some of the general guidelines of their imam apply, or it has something in common with a similar issue that is referred to in the books of the madhhab… and it is permissible for them to draw an analogy between novel issues that are not mentioned in their books of jurisprudence and those that are mentioned, in cases where there is no difference between the two issues, on the basis of what the imam of his madhhab said or what the mujtahids [senior scholars] of his madhhab said.
End quote from An-Nafahat `ala Sharh al-Waraqat, p. 160.
III.
Assuming that your teacher has reached that level, you do not have to ask her unless she is the only such scholar in your town. But if there are many qualified people, you may ask whichever of them you want, so long as he is qualified to issue fatwas and is a virtuous scholar, religiously committed and trustworthy. Moreover, you do not always have to refer to the one who is most knowledgeable and most virtuous, because among the Sahabah (may Allah be pleased with them) there were virtuous people and others who were less so, and there were among them ordinary people, and the ordinary people would ask a knowledgeable person of lower status, even though there were others of higher status, without anyone objecting. This clearly indicates that the ordinary Muslim and the one who is seeking a fatwa may choose between a knowledgeable person who is virtuous and one who is less so.
As for her saying that it is not right for you to differ from her, this is not true. It is not permissible for the one who seeks a fatwa to act upon it as soon as he hears it from the mufti if he is not quite sure about it, or he thinks that the fatwa is not really applicable to the matter in question, and that this fatwa of the mufti will not save him from the punishment of Allah, if the situation is as he thinks (that the fatwa is not applicable), as in the case when the judgement of a judge in his favour will not benefit him if he thinks that he is not in the right.
The Prophet (blessings and peace of Allah be upon him) said: “I am only human. You refer disputes to me, and perhaps one of you may be more eloquent in presenting his argument than another, so I rule according to what I hear. So if I rule in someone’s favour concerning the right of his brother, let him not take it, for I have only allocated to him a piece of fire.” Narrated by al-Bukhari, 7169; and Muslim, 1713.
The one who seeks a fatwa should seek a second and third opinion, until he becomes certain, if the reason why he is not certain of the fatwa is because of the mufti, such as if the one who seeks the fatwa believes that the mufti is ignorant, or because of complaisance in his fatwa, or because he did not base his fatwa on the Quran and Sunnah, or because he is known to be one of those who give fatwas based on trickery and loopholes and looking for ways to give concessions that are contrary to the Sunnah, or other reasons that make him not trust the fatwa of that man and he does not feel at ease with it.
See: I`lam al-Muwaqqi`in, 4/254; Sharh al-Kawkab al-Munir, 4/574.
Moreover, in issuing his ruling, the mufti is acting as a spokesman telling what Islamic teachings say, but his fatwa is not binding on the one who asked for it.
An-Nawawi said, narrating from Ibn as-Salah in Adab al-Fatwa wal-Mufti wal-Mustafti (p. 19): The mufti should be like a narrator, meaning that he should not be influenced by a close relationship or enmity, or be motivated to bring benefit or ward off harm, because the mufti is in the position of a narrator of what Islamic teachings say, which has nothing to do with any particular person. So he is like a narrator, not like a witness, and his fatwa is not binding, unlike the ruling of a judge. End quote.
With regard to the issue of whether a fatwa is binding, Ibn as-Sam`ani said in Qawati` al-Adillah, p. 147: If the one who seeks a fatwa hears the answer of the mufti, he is not obliged to act in accordance with it unless he commits himself to do so, whereupon it becomes binding by virtue of his committing himself, not by virtue of the fatwa. And it may be said that it becomes binding as soon as he starts to act upon it.
And it was said that it is binding upon him if he feels that it is sound and correct, and this view is the correct one. End quote.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said: If a Muslim is faced with a novel issue, then he should seek a fatwa from one he believes will give a fatwa on the basis of the Quran and Sunnah, no matter which madhhab he belongs to.
It is not obligatory for any Muslim to follow the views of any particular scholar in everything he says.
It is not obligatory for any Muslim to adhere to the views of any particular individual in everything he says except the Messenger (blessings and peace of Allah be upon him); rather the view of any person may be accepted or rejected, except that of the Messenger of Allah (blessings and peace of Allah be upon him).
If someone follows the view of a particular person because he is unable to find the shar`i verdict from anyone else, that is only permissible [and not obligatory] for him, and it is not something that is obligatory for everyone when it is possible to find out the shar’i ruling in a different way.
In fact, everyone must fear Allah as much as he can, and seek knowledge of what Allah and His Messenger have enjoined, then do what is enjoined and refrain from what is prohibited
End quote from Majmu` al-Fatawa, 20/208-209.
Conclusion:
If your teacher is qualified to issue fatwas – which is something that is rarely found, especially among women – then you may follow her and accept her verdict.
If you want to differ from her because you want to follow someone else who gave you a fatwa, who is equal to her or more knowledgeable than her, and has greater knowledge and is more qualified to issue fatwas, there is nothing wrong with that either, and you do not have to commit to following her fatwa and feel that you cannot do otherwise. This is assuming that it is appropriate to follow her view in the first place.
And Allah knows best.