Baby doesn't seem to like breastfeeding?

I notice that in the same amount of time on the breast she only gets half as much as my baby does when I give her a bottle. (About twenty minutes) Both her pediatrician and the IBCLC are throwing up their arms in confusion because the latch is good in both of their opinions and they don't seem to have anything else for me other than that in terms of advice. Now she's been rejecting nursing entirely about half the time for the bottle and I don't know what to do because I keep being told that everything looks fine even though it's obviously not since the only way she's been putting weight on is with pumped bottles and not me.