I give my eight month old around eighteen ounces of baby food a day. is this too much? how many ounces of baby food should she be eating a day?

Depends on the food: An eight month old requires between 100 and 120 calories per kg of body weight per day. Take your baby's weight, divide by 2.2 and then multiply by 100. That will give you the calories required. Then look at the calories per ounce on the baby foods and total them up. Babies will usually not take too much if allowed to stop on their own.

I agree with Dr. F.: Just respect your baby's food cues, read labels for nutritional information, allow her to finger-feed & continue breast-feeding till at least 12 months. You can hold a 2-handled open-mouthed cup for her to drink water from around 10-11 months & she'll be ready to wean to a cup before 15 months if you choose. Read "How To Get Your Kid To Eat But Not Too Much" by Ellyn Satter before toddlerhood.