Starting school is a big stressor and can deplete children very easily. This results in diminished tolerance for frustration and in disorganized behavior. You are managing the tantrums pretty well, but need a bit more of a systematic approach. If you rely on Lynn Clark's approach in SOS help for Parents you'll do fine (see www.sosprograms.com).
I would say that going to school has altered her familiar routine. Throwing tantrums and physical violence needs to be dealt with right away, as you well know. The best thing you can do if she starts hitting/kicking you, get down eye-level with her and say (very calmly but firmly, you can hold her still) " i need you to calm down, and when you are calm we will talk". She wont like it, but remain calm and firm, and keep putting her in time out, perodically askin "are you calm enough to talk yet?" If she continues to fuss, remind her that until she calms down she will have to remain in timeout. Once she is calm, make eye-contact again and say something along these lines: i know you are upset, and I'm not sure why, but you cannot hit or kick me. That behavior is hurtful, and I will not tolerate it. If you keep doing it, you will have to calm down again, and then we will talk about why you are upset. Dont say things that she could answer with yes or no. Keep it as simple as you want, but emphasize that her bad behavior will lead to a timeout for her to calm down. Hope this works for you! If you can, watch Supernanny and Nanny 911. Their technics are amazing, and they do work! Good luck!