We praise Allaah for guiding this sister to embrace Islam, and we ask Him to make her heart steadfast and to increase her in faith and certainty.
We advise her to tell her parents or not to tell them, depending on the consequences of either action. Will that lead to them disowning her without throwing her out of the house or harming her? Or do they have the power to force her to go back to their religion or not?
Whatever the case, if telling them will lead to bad consequences for her, then we advise her to delay that until her faith is stronger and her knowledge increases. We also advise the Muslims who are aware that is Muslim to find a righteous husband for her and to prepare a suitable place for her in the event that she has to leave her parents.
The fact that her parents may think that she has become Muslim in order to marry a particular person does not matter, and there is nothing wrong with her getting married if that will give her protection and help her to adhere to her religion.
You should consult people of knowledge and experience in your country who know about this sister’s situation and that of her family, and their circumstances.
And Allaah knows best.