Sometimes, love can cause a person to view a person through a different mindset--"rose tinted glasses," if you will. She may be so emotionally attached to him that she is blinded to the less positive realities about him.
Of course, she could also be in denial--she may not want to admit that he is not the "perfect" person that she would like to believe that he is, so she tells herself (and, of course, others) what she wants to believe rather than what she actually believes so that she can convince herself that "all is well."
At any rate, I wish your family the best of luck in dealing with this situation.