Hi M.,
I totally agree with Daniella and Melissa. Give her very limited choices, and soon the phase will pass.
My youngest got really carried away when she learned the power of "no," and although she tried my patience ALOT of times, she eventually realized that saying no got her nowhere, but helping herself by helping me to take care of her, was much more fun.
She wasn't fully potty trained until she was 3. She would number 1 on the potty, but not number 2. Finally, August 2002, we were playing in the pool and she said "Mama, I have to go poo-poo." She said it so quietly, that I almost missed it, but every single day before that, I offered her the option to go poo-poo on the potty and she adamantly refused! "NO!" was her favorite way.From that moment forward, she was totally potty-trained, and quit telling me no when I asked if she had to go poo-poo.
Just offer choices, if she has a tantrum, ignore her(it will be hard sometimes, but you can do it), and maybe put a bike helmet on her(I read this idea on another thread--great suggestion!) for those times she bangs her head or hits herself. She might stop if she hates wearing it or hurts her hand hitting the hard helmet.
Good luck! You both will get past this, and then it'll be something else lol. ;o)
K. W