B.M.
Hi Serena,
Congratulations on your little girl. I know the dedication it takes to pump (I pumped for my first son for 14 months - he's 3 1/2 now).
I know that each baby is different. My 9 month old is also breastfed, but 1 day a week my mom babysits and he takes a bottle on those days. He only takes 2 bottles from her and those are each 6 oz, so its only a total of 12oz. I always leave a 3rd bottle with her, but he doesn't always take it. I think too that when taking a bottle, they take in more air than with the breast, so they may feel fuller faster (that's my educated guess).
I don't have any advise, but it sounds like she is doing ok. My little guy is a chunky boy, so its not like he's missing any meals! :-)
I think I always worried if he was getting enough. If she's doing well with the bottle, let her determine how much she will take. If your breast is available at night, she will make up for anything that she didn't get during the day. As you know, breast feeding isn't just about nutrition, its about the closeness and bonding, so enjoy the time that she is at your breast at night.
I hope my babbling was helpful. All this to say, I wouldn't worry too much, it sounds like she's doing pretty well!
B. :-)