jb_miraval This lastexception is kind of all over the place. There are some career-related errors, and some that don't look like they're career-related, and one that's related to an issue with modded items used for developmental milestones. For the last type, this mod can help:
https://www.patreon.com/posts/mod-milestone-81237568
Aside from that, I'd suggest adding the teenager to an inactive household, then visiting her and aging her up (cheat, birthday cake, whatever). See whether you can load her once she's a young adult. If you can, but you want her to be a teen again, enter the cas.fulleditmode cheat and take her into CAS, where you can change her age. The idea is that aging her up would (hopefully) drop her school data, which would then revert to the default once she was a teen again.
Since this is experimental, keep a backup copy of your save.