@ItzHarri As far as I've read, the grounding process is still bugged to some extent. (There was recently a thread about a sim who was grounded as a teen and was still using the "sneak" style walk as an almost-elder.) I take it this is not an issue of slacking off—your sim's doing her homework and is in a good mood at school? You can try clearing the five cache files in your TS3 folder in Dcouments, but it may not help. The files are: CASPartCache.package, compositorCache.package, scriptCache.package, simCompositorCache.package, and socialCache.package. (Don't worry if you can't see the .package extension; they're still the same files.)
In a vanilla game, if clearing the cache files doesn't help, there are probably only two other good options. The first is to move her out of the house, wait for a sim-day or so (save and then quit while she's out, and clear your cache files again), and then move her back in. You'd have to send an adult with her, but for this purpose you could always move in a random one in Edit Town. The other option is to evict her whole family and move them back into their house in one Edit Town session. They'd keep their jobs and relationships but lose their promised dreams and opportunities. I suppose you could try just splitting the household and thus temporarily evicting the teen and an adult as well. But if that doesn't work either, it would be best to evict the entire family, save the house to the bin, bulldoze the lot, replace the house, and move the family back in, all in one Edit Town session.
It's possible that testingcheats would allow you to drag up the school performance bar (I've never tried that), but it wouldn't fix the grounding issue.
When you start troubleshooting, it would be good to first use "save as" and change the name to generate a spare saved game on which you can experiment. This way, when you're trying different approaches, or if you don't like the results of one of them, you have an unaltered save to which you can revert.
