My daughter did this too once in daycare - I really think it was because she was watching the older children. I would give it to her in a sippy cup and she'd down it...in a bottle she'd refuse. She wanted to be a "big" girl.....maybe try out of a sippy cup?

((BTW just making a statement, it irks me to no end that people automatically think bottle = formula. Breast Milk can come from a bottle too if mom pumped, no? I hated when the IDIOTS would smugly say "a bottle...oh no, I give my child b.milk" to where I'd respond with "not that its any of YOUR business and I don't remember asking YOU stranger for your advice or comments, but this IS breast milk." sorry, hits a nerve))