There are a few things that could be going on. You did not say how long this new living arrangement has been going on for nor did you say if your fiancee's daughter lives with you full-time. I am willing to bet that she does not know why she is hitting others (most kids her age do not understand why they do things). She may be trying to get attention (even negative attention is better than no attention), although you were giving her attention during the second incident mentioned. She may be afraid that she will lose attention once the new baby is here and reacting to that. It seems to me that there have been a lot of changes (and coming changes) in her life and she is trying to process the changes but at 5 does not have the skills or knowledge on how to do that. If possible I would see if you can get her into play therapy to help her process the changes.