We actually resolved this issue on our own, but I wanted to let you know how we did it In case it helps other people.
My daughter did change her email address at one point. The problem was, before she changed her email address she had stopped sharing her purchases. That was still toggled on when she changed her email so that setting remained for any of the songs purchased under the old email address. I found a spot under the sharing settings that said “Share using a secondary email Apple account…” She clicked on that, entered her old email address, enabled sharing purchases and they all reappeared in the music app. Crazy but it worked. I appreciate your advice either way. It set us on the right track to solve the problem. 🙂