Is a girl's supplication for the young man she loved and became attached to to be her husband, knowing that he is married and she had previously refused to marry him, considered a sin?

There is no reason to reject a suitor who is religious and of good character, even if he is married, because polygyny is permissible under the condition of justice. There is no sin in a girl supplicating that a man be her destiny. We advise entrusting the matter to Allah, for Allah is more merciful to her and will choose what is good and righteous for her. And perhaps not marrying him is a good that she does not know.