I can sympathise with your embarasment but your willingness to talk about this has spurred me to write this. At about the same age as your daughter I often did the same with my family pet. For me looking back I would have to say i did it because I didnt think myself worthy of human atention. I would have been mortified if i had been caught and think it may be worth talking to your daughter to see if there may be an underlying cause without berating her for her actions, knowing how much you diagree with it may mean it is now a cry for help. Punishment will only reinforce the feeling of self loathing. I eventually stopped when my self confidence and opinion of myself increased.