My almost 3year old is very strong willed as well. The best thing I can suggest is to calmly explain to her why she can't do something. When Sierra refuses to wear a seatbelt, I tell her she has to wear it to "Be Safe". This is quoted directly from Dora the Explorer, and she somehow believes her. If I can relate a reason to one of her favorite TV characters, it somehow makes more sense to her. We also have a tough time with her being demanding. So when she does ask for something nicely, she gets praised with "Great Job" or "Thank you for asking so nicely, that's awesome!" And when she forgets and demands something, we say "How do you ask for more milk?" or tell her to ask in her "Happy Voice". She will then phrase it nicely. Her first 6 months of being 2 were hard, but then it gets easier. Good luck!
Routine, routine. Stay firm and consistant. That is what I am being told about my triplet boys, but sometimes it is much easier said than done.Good luck-let me know if you find something that works.