She can’t afford to move out, but can she afford to pay any amount of rent?

She is basically your tenant, so have her sign a rental agreement and charge her monthly rent. There are plenty of boiler plate formal Owner/Tenant rental agreements to be found on the web, so don’t just make something up. For you, it advances your daughter a step towards independence. For her, this does not seem like such a bad deal, given the alternative of paying a lot more rent to a stranger who will be much less tolerant of her behavior.