You hurt her to teach her not to hurt others? I'm not sure that tactic will work sorry. I'd definitely suggest not smacking as it sounds like she is reaching out for outside support and you don't want this to affect your family badly.

With the accidents maybe making sure she is properly apoligised to will help? Not sure obviously how these are dealt with already but maybe she feels they are brushed over and her pain is not acknowledged.

Good luck! When I was little I had a baby doll that would cry when you took it's dummy out. I would take it out in public and slap the doll around the face, tell it to be quiet and put the dummy back in. Certainly behaviour that never happened in my family so my poor Mum would bear the brunt of some terrible glares for nothing!