Why is our daughter not feeding enough volume orally?

How often does she eat when fed orally? If shes eatting every 1-2 hours thats a good amount really...she needs 24 oz in 24 hours....does she get that when feeding orally?? When fed orally is she getting enough wet/messy diapers daily?? as in 6-8 wet or messy ones, really wet being 2.