Non-demon Molly will not get fired for anything. I have enslaved her through transforming into Jane and finishing that plotline to enslave Jane, then talked to Molly in the store about free items. I have bought 2000 health potions in total (took about an hour), but she doesn't seem to run out of money. The dialogue about her covering it does appear on each purchase.
Is there any other requirement to get this to happen? It's infuriating.