back with an update, in case anyone is curious! grilled cheese aspiration is complete. finally got a neighbor sim into the apartment to eat the cowplant cake twice. i turned off my few mods and also testing cheats, but that's all i changed. i have NO idea why that one sim was immune to literally every form of death... if anyone ever runs into that issue again i'd be interested to hear about it!
anyway. in celebration, here's a pic of my sim fulfilling the lofty ambition of telling Hades, King of the Dead, Reaper of Souls, how delicious grilled cheese really is. thanks everyone for helping~