I wouldn't drop the bottle size - if she decides she wants the whole lot it won't be there for her! If it's only been going on for a few days it could well be teething and she should increase her intake again.
Babies normally drop to 3 bottles around 9/10 months so a bit early but it could be that this is what you need to do to protect her milk intake.
I would keep offering bottles as normal, try the teething gel as PP suggested, for a few days and see what happens. If she is still refusing it may be worth trying 3 bottles to see if that increases her intake again.
Laura