E.T.
I used the Medela bottles and nipples. My daughter disliked the Playtex ones.
Otherwise, my daughter would eat if she was really hungry, but otherwise would wait for me to return.
For daycare, she never moved past little bottles and for an entire day would usually only drink about 8-10 oz. When I brought her home, she nursed.
My best guess is it is a combination of not being hungry and not liking the bottle. If she drinks 2 oz from the bottle, she takes the bottle.
I wouldn't worry.