DD turned 3 in May and, for the most part, is great with her 11 month old brother. HOWEVER, she is acting pretty aggressively towards him whenever I turn my back. It started as an issue over toys once he became mobile. She would snatch a toy out of his grasp or try to hold him back as he moved towards one. Now it's escalated to her pushing him down for no (apparent) reason. I have witnessed her shoving him by the back of the head, face first into the floor, as he's attempting to crawl. She won't do it if she's knows I'm watching, but it's almost guaranteed that she will inflict pain upon him once I leave the room.
Today she slammed his face into the ground, and when I asked her what happened, she was laughing hysterically. I've been trying to calmly explain to her why we don't hurt others and she knows that it makes her brother sad. She obviously gets that it's undesirable behavior because she waits until I leave to do it. Is this just a normal phase or am I missing something here? I feel like I'm just repeating myself yet the aggression is escalating.
Is this a typical cry for attention? I try my best to spend quality time with each of them, but certainly understand her feeling frustrated over the time spent with her brother. We've started co-sleeping with her again just to make sure she doesn't feel excluded. Any other thoughts?
Also, any recommendations for children's books that may address some of these issues? We read a lot of the books pertaining to having a new baby in the house, but nothing in the way of older sibling issues.