Hey Olive

If it was me, I wouldn't be too worried at her age. But thats very easy to say I know!!! Sorry! Is she really skinny? I'm really think that she'd be super cranky and miserable if boobies weren't enough.

If she's not big on eating large amounts, then I would just make sure she is having a lot of small tastes of a wide variety of foods. Even if she isn't eating a lot.
We have found with our DS that he really hasn't been interested in eating much food. Not in one sitting anyway. As a result he is on the smaller side (weight wise) and you really see his weight gains slow dramatically from 6-12 months. BUT in the last few weeks he's really turned a corner and wants to eat and eat! So I wonder if your DD will do something similar?

If she looks healthy and seems happy, I'd just continue as you are. Unless the amount of boob is really bothering you. I honestly think that at some point she will start to want more food, she just may want to do it in her own time IYKWIM?