Is it permissible to pray for the dissolution of an engagement so that the engaged girl may be married to another person, given that her current fiancé is among the people of innovation (Ahl al-Bid'ah)?

If the man proposing to the girl holds an innovated belief that amounts to disbelief (kufr), then his proposal is invalid, and it is permissible to supplicate that he leaves. If his innovated belief does not amount to disbelief and she has not accepted his proposal, then it is likewise permissible to supplicate that he leaves. However, if she has accepted him, it is not permissible to propose to her over his proposal, nor is it permissible to supplicate that she leaves him. If there is no way for you to marry her, then leave her and ask Allah to provide you with a righteous wife. It is incumbent upon the guardian (wali) not to marry off his daughter except to one who possesses religiosity and good character.