Note that it is permissible for a man to speak to a non-mahram woman, subject to important guidelines and conditions, the purpose of which is to prevent fitnah and sin. These conditions include :
1- That should be done without being alone with her (khulwah).
2- That should not go beyond permissible topics.
3- There should be no fitnah (temptation). If his desire is stirred by talking to her or if he starts to enjoy it, then it is haraam.
4- The woman should not speak in a soft manner,
5- The woman should be wearing full hijaab and be modest, or he should speak to her from behind a door. It is better if they speak on the phone, and even better if they communicate via letters or e-mail, for example.
6- That should not go beyond what is necessary.
If these conditions are met and there is no fear of fitnah, then it is o.k. And Allaah knows best.
Shaykh Saalih al-Fawzaan said, in his answer on the ruling about young men speaking to young women on the telephone: “It is not permissible for young men to speak to young women because of the fitnah involved, unless the girl is engaged to the man who is talking to her, and they talk only about matters pertaining to their engagement; but it is preferable and safer for him to speak to her guardian about that.” (al-Muntaqa min Fataawa al-Shaykh Saalih al-Fawzaan, 3/163, 164).
You have not proposed to this girl yet, so you have to be very careful and avoid exposing yourself to the causes of fitnah by taking all possible precautions to achieve your goal without approaching this girl.
The basis for this is two aayahs from the Book of Allaah:
1 – “O wives of the Prophet! You are not like any other women. If you keep your duty (to Allaah), then be not soft in speech, lest he in whose heart is a disease (of hypocrisy, or evil desire for adultery) should be moved with desire, but speak in an honourable manner”
[al-Ahzaab 33:32 – interpretation of the meaning]
2 – “And when you ask (his wives) for anything you want, ask them from behind a screen, that is purer for your hearts and for their hearts” [al-Ahzaab 33:53 – interpretation of the meaning]
Finally I would like to remind you that the Muslim’s standards when choosing a wife should be the standards encouraged by the Messenger of Allaah (peace and blessings of Allaah be upon him) when he said: “Choose the one who is religiously-committed, may your hands be rubbed with dust [i.e., may you prosper].” (Narrated by al-Bukhaari, 5090; Muslim, 1466).
And I warn you against everything that may lead you into doing haraam things or bring you close to that, such as being alone with her, going out with her, etc. I ask Allaah to make it easy for you to find a woman who will help you to obey Him.