HELP!! 4 year old behaviour issues?

My daughter will be 5 at the end of May. since she was about 2 my husband and i have had some problems with her behaviour. it has gradually got worse and this week has been the worst. she backchats, pulls faces, laughes at us, bullies her 2yr old brother, smashed things around my house. normally when i say no to something but it can b over something silly like not giving her the food she fancies when she hasnt even told me what she wants. she is in the reception class and was great for her first yr in school but things took a turn for the worst before xmas 2010. she doesnt listen to the teachers at all to the point they are having her hearing tested by the school nurse asap she laughs at the headteacher when she is told off my him, she refuses to participate in story time (sitting still on a mat while the teacher reads a story) she will not stand on the naughty spot in the yard, she pulled her best friends hair that a chunk came out, she jumps all over her friends and hugs n kisses strange children (someone she would have just met in the park minutes before) on tuesday she was sent to the naughty spot and wouldnt stay there and ran off and slapped her best friend across the face in front of a teacher, she has had screaming tantrums in school that she has been sick and they loose all control and she kicks on the floor so they cant get near her and if they try she will kick them, on thursday (yesterday) they were doing group play and she threw a rock which split someones head open!! and today she lay in the middle of the floor trying to trip all the children up. i know this is all bad behaviour but i am extremely worried because she doesnt seem to care about the things that she is doing. it has got very dangerous now tho, she will wriggle out of your grip and run across roads, jump from an 8ft slide and come down the stairs on her belly. we are petrified something is going to happen. she cannot be taken anywhere there are lots of people because she goes mad. she jumps everywhere and cant keep still for a moment. she doesnt stop talking and nagging. she has a brilliant appetite and will eat any fruit or veg at all. she is never given fizzy pop, sweets, crisps or chocolate. she goes to bed at 8pm and wakes at anytime after 3pm. this has only been for the last 2 years. she is constantly tired but denies this. i think most of her problems come from the fact that she is so tired but we have tried helping with the sleep along with the health visitor and sleep therapists but nothing is working. whatever dicipline we try, naughty step, time out, time in bedroom, taking away toys, shouting, nothing is working. we are desperate for help and to know is anyone else going through the same thing. the school have now got a behaviour officer involved but have said it could take months for her to be seen. i am not happy to just leave this drift for months because i am scared whatelse can happen. she is a lovely little girl and she has lots of cousins, aunties and uncles and everybody loves her to pieces but no one can understand why she is doing this. we are extremely desperate for help as she is so clever we dont want teachers writing her off as a "naughty" child and her falling behind. also her teacher said that she is now starting to isolate herself. does anybody have any ideas what could be wrong. we are starting a behaviour mangement programme run by the health visitors to hopefully get some tips.