The advice I was always given was to feed to appetite. I'm pretty sure my two were both taking 4oz feeds at that age, sounds pretty normal to me! I wouldn't worry too much about working out the amount of oz - that is a really rough guide and every baby is different. If she is keeping her feeds down and has the appropriate wet and dirty nappies she is taking what she needs. Don't forget if she is draining feeds you need to increase the bottles so there is enough for her to stop because she is full not because the bottle is empty.
I think the first few weeks are a permanent growth spurt!
HTH!
Laura