I am sorry?
She is laying hands on your daughter and you do nothing?

Have her charged with assault, that might at least wake her up for a minute, if you were hitting her and your kids would anyone think twice about telling her to leave you or press charges.
I don't understand how this is even a thing. You don't hit your kids in anger. It's assault.
Also what does this teach your daughter about boundaries.
It's ok to be with someone who hits you?

Sorry but this is not a healthy environment for anyone.