How do I know when/if my 3 yr old needs prof. help?

A bit of jealously is normal, and wanting attention. Either she is a very mature 3 year old and is aware of her actions, or as you know these are symptoms of Bipolar-tantrums, sleep disruption, agression. Give her a little more time-try spending a little more time with her- see how she acts in another 2-3 months. If she gets worse, I would have her looked at to see if she has Bipolar traits, outside the current situation.