A balanced diet consists of protein, carbohydrate, fat and water. Peanut butter is an excellent protein source, as long as it is on a grain. Bread provides carbohydrates and B vitamins. Substitute the jelly with a fruit spread, add some fruit or raw vegetables and low-fat milk and you have a very balanced, nutrient-dense meal. Metabolically, her body doesn't care if she gets her protein from peanut butter, tuna or lunchmeat, so you can feel confident that she will continue to grow on PB and J!
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.