always, always, always, confront with a witness for the sake of keeping the peace... I am a mom, and like any relationship, without communication, there is room for the enemy to have his way...
Prayer has a way of changing a persons heart and mind, especially when your in the will of God. Seek God concerning this matter, and then like others said approach her on it, but only with a witness so mess will not get started beyond that which is already in place.