Another thought to consider...
She rides the bus to go wherever? To my knowledge, buses usually do not allow pets on board unless they're handicapped assistants. How would she transport a sick animal to the vets, assuming she could get vet care?
While I understand her needs, love isn't as much about your (her, in this case) needs as it is about caring for another and their needs. No cat needs to be in a place/home that cannot be depended upon to really care for the cat when it's called for.
If she truly desires to have a cat, then let this desire be the motivator for her to improve her financial circumstances in whatever way she can to make her dream come true.
Callie