R.D.
As another poster said; trust your instincts!!! But also, trust your child's instincts. At her age, she is incapable of over eating (unless you are force-feeding her) or under-eating (unless there's an illness or you are depriving her). To babies, food is just food (whereas for adults sometimes it's comfort, sometimes it's the enemy). So if she tells you she's hungry, she is, if she doesn't want to eat any more, she's full.
Also, keep in mind that breastmilk or formula are supposed to be the main source of nutrition for the first 12 months - one recommendation I've always recieved is offer breastmilk/formula first, and if she's still hungry, THEN offer her solids. I breastfeed, so I don't know about formula, but with my children, I let them nurse until they decided they were done. If they still seemed hungry, THEN I fed them solids.