I never took up a fancy in learning about molting. In fact, all I care about is that if they're losing a load of feathers, I'll just say "Oh, it's that time of year again" and make a mental note because I was told that molting inhibits breeding. I'll also bathe them more often. So, yep, I'd say your baby was just molting her tail feathers. Divine came to us with her tail feather like that and it fell off after she flew to a perch.