If that is all she eats, i would be fairly certain she is waking from hunger.
At 9 months, you really want to be expanding what she eats to include protein, fruit/veg/ and carbs at each meal. Granted, it will be in small amounts but you are going for the variety really. Also, would be a really good idea to start having some finger foods. Baby cereal is fine when just starting out but it is generally just filling with little in terms of varied nutrition. I certainly would limit it to once per day (breakkie).
Her formula intake would be fine to drop to 20-24 ozs in 24 hrs as well.. right now she a little higher than that during the day hours without considering night feeds on top of that.
This is a typical feeding routine for this age - think it could work for you? Using this routine, each bottle is 7-8 ozs.
** taken from:
Sample routines for dropping bottles (daytime core hours only)E: 7.00 wake up and feed milk and breakfast
A: 7.30
S: 10.00
Y: your choice
E: 12.00 lunch
A: 12.30
E: 1330/1400 milk *dependant on your LO’s nap time
A:
S: 2.00
Y: your choice
E: 4.30 dinner
A: 5.00
E: 7.00 milk given before or after bath
A: bath
S: 7.30 bedtime
What do you think? As an aside, I agree with Laura (Lolly) that the best way to wean night feeds is to reduce volume not dilute what you offer - the reason is this: some babies will wake for the full feeling well beyond the need to eat... and when the case is that they don't need the extra calories, they are already waking for habit not hunger... reducing eliminates these concerns.