I'm a Love and Logic mom, so I'll share with you a Love and Logic Idea.
After 1 warning, I'd snap the child up in my arms and sing the Oh-Oh Song "Oh-Oh, a little bedroom time comming up here - This is so sad" and by time you say sad, she is in the room, You can offer a choice, "Door open? or Door Closed?" She may answer with a toy up against the head, but that means 'Door Closed',
Be sure to smile big and sing the Oh-Oh song, then smile and say "you can come out when your sweet", From the very moment she is calm, set the timmer for what you feel is age appropriate and when the timmer goes "Ding" she can come out. Continue about your business when she comes out, dont tell her what she should have learned, She's very smart, she'll know.
After a while, she'll just know when Mom sings "Oh-Oh", she know's mom means business, not 1-2-3 strikes your out, just 1 strike and your out.
Some kids will just go screaming into there room, mom doesnt need to take them in there anymore when they sing the "Oh-Oh" Part of the Oh Oh song. (Its so cute)
Now remember, any child worth keeping, when you sing Oh'Oh, will give you the sweet eyes and say "Ok, I learned, I'm sorry"
But if they know better, do you let them manipulate us with those sweet eyes? Thats up to you. if it were me, I'd say sweetly "Oh good, I'm so glad you learned and are sorry, that means you'll be out of your room very soon" and off they go.
There will come a day where you wont need the "Oh Oh" song much anymore, that first warning will be enough.
Fore funny parenting stories from the Love and Logic Institute, go to http://www.loveandlogic.com/audioclips.html
I think there is an example of the Oh-Oh song there, and some other great stories so you can see what Love and Logic is more about.
You can also buy books and CD's on that site, or even E-bay. I got a great one called "Love and Logic Magic for Early Childhood".
GL and have fun.