[null and void]

I don't know how a mother can defend a person who does that to her child .. this is beyond my comprehension.

Any number of reasons. "Love". Fear. Her own personal history of abuse. Insanity.

Also under law in most states, a wife or husband may not be compelled to testify against a spouse.

[CyberAnt]

Well .. the laws aside .. I guess the possibility of her own abuse is a reason, plus she was the only girl.

At least she's with the Lord - which is a vastly better place than her parents provided for her.