Hi J.!
I am almost embarrassed to type this, but we went through this same thing with my oldest DD (who is now almost 6) - when she was THREE. going on FOUR. It was ridiculous!
My advice to you is this:
a.) realize that she WILL wean off the bottle eventually! It seems like forever now, but in a year or two or 18, you'll look back and realize how short of a time it really was that you "battled" over the bottle. Plus, you'll WISH it was as simple a fight as just a bottle at bedtime!
b.) We started doing a VERY watered down bottle for her, not cold turkey, but slowly putting less "milk" in it, and more water. Till eventually it was just water. Then less water. Then less water. And finally she was just getting one or two quick drinks from it and realized it wasn't worth the effort.
If you are really more worried about keeping your great bedtime routine intact, then don't worry so much about the DATE that she gives up the bottle. Emphasize that she will be a BIG GIRL who doesn't need the bottle, and stop mentioning the night time bottle, but don't make it a huge ordeal. One day she just won't need it!
Ok i am typing a novel here, sorry.
Best of luck to you with the weaning!
T.