J.R.
Seriously, I know it sounds harsh, but you have got to be the parent. I'm in your same boat. My 2.5 year old would rule the roost if I let her. And I am in a constant power struggle with her. But at the end of it all, I am the Mom and she is the child and what I say goes. Trust me, if you don't get it under control now, it will only get harder as she gets older.
Make sure you are spending quality one on one time with her during the day. I notice that my daughter acts out the most when I too focused on my daily tasks and I haven't given her some undivided attention. At least 30 minutes of sold straight through Mommy time usually cures any outbursts that arise during the day. It's a great time to read some books, do an art project, go for a walk, or just let her talk...even if you can't understand her. You know how girls are. ;-) We need to express ourselves and we need EYE CONTACT.
Good luck!!