If your child has pectus excavatum, can she ever develop normally later in life?

Yes. Pectu excavatum in children is never self-correcting. It can be mild to severe and effect exercise tolerance, self image, etc. In girls it can affect breast development and orientation. This can pose certain psychological issues. Some children weather these well and other less so. A simple evaluation by a pediatric surgeon can answer all yours and your child's questions.
Absolutely. Pectus excavatum is a cosmetic defect with zero effects upon a child, s development. The only exception, which I have never seen, is if it is so severe that it impinges upon the expansion of heart or lungs, causing problems. Your doctor can determine if this rare side effect is present.