If he doesn't have fleas anymore she probably used it. Because they don't just go away on their own. I'd imagine if she doesn't repeated the treatment there will still be fleas in the house.
Babaloosha sleeps in Sheila's room, she could also take him to the vets and doesn't.
Yup, they're both responsible for him, wasn't it Sheila that took him from the streets? Cats want comfort, but they also need the basics like a good diet, a clean litter tray ect