Aw, nakaka-stress talaga yan! A few of us moms noticed the same thing around that age, sometimes it's just a phase or they're getting picky, pero it could also be something with the formula itself (like kung bago yung brand o batch) or even teething discomfort na nag-affect sa appetite. I'd suggest checking with her pedia asap to make sure walang underlying issue, especially since it's such a sudden change from 5-6 bottles a day, hindi normal ang ganitong drastic shift. In the meantime, try mixing the milk sa food na alam mong kakainin siya, like sa cereal or pudding, so at least nakakakuha sya ng nutrients; one of my mum friends also tried offering it sa ibang cup or bottle to see if it's just a mood thing.