Also, children do what works. I am an educator, and have training in child behavior. All children have a trigger. Find what she prizes, and use that . For my child it is her TV time. For others it may be video games or a special stuffed animal. ( I know it sound mean, but she NEEDS to know you mean business.) BE CONSISTENT!!!!!!!!!!! If you give in at all she'll know you'll cave and the behavior will continue. Make sure all caregivers are on board with your plan. If Grandma gives in or Dad sneaks in tv when Mom said "No", it will only send mixed messages, and undermine the discipline.Remember you are the adult, and it is not fair to her to be able to call the shots. She will feel SO much more secure knowing someone else is making decisions for her. Her behavior may escalate in the beginning as her frustration grows, and to see where the" line" is, but stick with it. Take care of it now when she's 5. It only gets harder as they get bigger. Good luck!
If you've tried behavior modification with no success, ANDd the behavior is the same at home and at school -- then its time to take her to a doctor for an evaluation. She could be suffering from anxiety, or some other type of issue. I suggest you take her to a psychiatrist who specializes in children so that the dr can help you and the school build a plan that will work for her.