Kinda hard to explain, but hopefully pictures will help:
This is mostly only happening with the body and main hair part. All the other parts (pigtails, eyebrows, etc) work as usual. The pigtails and eyebrows are paths, but the other parts are not. The eyes, teeth, and eyelashes aren’t mirrored. Also, for some reason, the way I modelled some of my other character worked, even though I don’t remember doing anything differently.
I noticed this when I was trying to use the X mirror option once I applied the mirror modifier. It wasn’t working across each half of the body, but did work with the body mirrored under her feet.
I feel like I just have to flick a setting or something to fix it, but I don’t know where to do that.