I think if she's admitted to you that she's at the end of her rope and has been abusing her daughter (which over discipline is in my opinion) then I'd definately call. Someone has to speak up for the child. I don't know how the laws are there, but is it possible that your complaint will get her into parenting classes to help her deal with a special needs child?

I'd call the father too, maybe he doesn't realize how desperate she is.