{{hugs}} She really could be that fast. Isaac was at that age. 3 things to look at: (1) Does she have enough wet diapers? (2) is she gaining weight appropriately? (3) does she seem satisfied after meals? If yes to all (and it sounds like it is), then you're doing just fine.
There are several things that start happening around this age that can make you afraid for your supply... lo's can get more efficient & therefore don't nurse as long as before. Boobs get "smarter" about how much your particular lo needs, so the make less excess. This can show up in reduced pump output. Don't worry. That's normal. Sometimes moms find that they need to shift to double-side feeding. (I fed double from day 1) All of that is normal, and as long as you have diapers, growth, & contentment, you're fine.
Just keep following her cues. If she still seems hungry, I'd try offering the other side rather than topping off with ebm in a bottle. That way, if it's a growth spurt (which often occurs somewhere around 3 mo), she'll be giving your body the signals it needs to make more milk. Also, a baby will almost always take milk from a bottle, even if they're not hungry. It just drips in their mouths, so no work is required.
Hope that helps. Keep posting back to let us know.
