If she's carrying on nicely with 4 hrly feeds, I'd say she's getting enough. I know a baby that liked to have 10-12 oz, so you can try, but 9 is probably just fine. If, however, she seems to be acting hungry, just give her another bottle when she wants it. You can be flexible with her feeds. She may want some feeds after 4 hrs, and maybe once or twice in the day be ready at 3.5 hrs, and then you could add a small top up before bed.