I agree with Megss--it's probably just a phase. I'd also assume that she's getting hungry again around that time (growth spurt), and just wants something that will easily fill her tummy. Hang in there. Our little ones can be so unpredictable! And do things for reasons of which only they know why, which can be so frustrating.
Oh, and what a terrible thing for her doctor to say! Sometimes I wonder why people choose the professions they do when comments like this are made..... I weaned my ds from the bottle at around 14 mo, so she's by no means "old" to have a bottle. I wouldn't worry about it. Do it when you both are ready.