It always amazes me that people do these horrible things and then claim they never realized how sick they were until they killed someone and then have to go to jail. I'm sick of hearing it...it was your own fault, your own decision, your own actions...now you can pay for it.
She knew that her daughter was physically large enough to retaliate against her if she tried to beat her daughter the way she wanted to.
So she decided to wait until her daughter was asleep, so she could get her revenge. And she waited for hours, then quietly crept into her daughter's room and hit her with a hammer.