all updates after mojave (10.14) drop 32-bit support for applications (ie. cave story), so they're not going to run anymore, i'm sorry. i believe there may be a port that will work, but i don't remember which one, you'll have to poke around the downloads page.
i may sound like a hypocrite here as i hate people suggesting this to me (i also use mac but i'm still running mojave), but is it worth looking into bootcamping her laptop if it has enough storage?
Thank you for the information! It seems I just hadn't read much into it
The NXEngine should work right? I can't really find the Mac Port for it, and the link on the tribute site brings me to a confusing Github page, so if you know anything about it, I'd love some help with that ^^'.
When it comes to bootcamping, I really don't think she'd be comfortable with adding so many things to her computer just to run cave story, she'd rather come here and beat it on my computer whenever she comes, but if there isn't any hope anywhere else, I'll just have to go with Wine honestly.
Thank you very much for your help! I'll try to find the Mac version of NXEngine in english, if there is any...