A lot of babies of this age still fall asleep with bottles - my oldest child always did, it can be quite hard to stop them if they are tired. Perhaps the only way you can get round it is if you give her the milk before she is really tired, so that it doesn't knock her out. But rest assured, children go through phases and they rarely last forever. Milk is a kind of sedative to babies, so naturally helps them to sleep at bedtime. When they get older, though, it doesn't have the same effect, and then they learn to fall asleep alone, after relaxing with a story or two. And when you take her off the bottle and give her a cup, I doubt she will fall asleep with her millk as the sucking motion isn't the same.
I had the opposite problem with my second child - I could never ever get him to drink from a bottle and even with a cup it can be a slow and arduous process - they all come with their little ways. I often wished my son would take a bottle just to knock him out, because he just stayed awake longer instead and I lost half my evening. Be thankful you have some peace and quiet - it might not last!