Then shift-click on the sim and select Edit in Create a Sim. To reach CAS, bring up the cheats console (crtl-shift-c) and enter 'testingcheatsenabled true' without quotes. The teen may have a broken outfit that's preventing her from aging up properly changing her clothes and hair for all outfits would fix that.
If that alone doesn't help, try reassigning her outfits in Create-a-Sim (or use NRaas MasterController's Stylist function, if you have the mod).
These caches should be cleared regularly even in the absence of any game issues, as they'll fill up with stale data. The first thing to do is delete the five cache files in your TS3 game folder in Documents.
