[ON] Difficult Client with Boundary Issues

Posting on behalf of my mother who doesn't have Reddit, but what are your thoughts on maintaining good professional boundaries with difficult clients? She has one she's currently struggling with that seems to think that because she's gifted us items in the past (mainly cheese which, yes, bizarre for the person cleaning your home but not the oddest thing our family's gotten in exchange of work), that she is somehow a golden client, and it isn't a big deal that she no longer can afford the services provided for her. My mother has been very gracious about this behaviour in the past, partly because she'd very against confrontation - clients have threatened her kids (me and my sibling) in the past due to raising prices - and wants to practise what to say before going to the client. Personally, I think this client may not be all there mentally anymore, and has been spending too much on frivolities, of which she occaisionally unloads on us because 'helping the poor is part of her beliefs', but its not my place to say that to said client aloud. Know what would help my mom? PAY HER WHAT SHE'S DUE!!! But I'm only here for advice on how to help my mom prepare for the initial talk they'll have soon. So:

What would you do in this situation? Drop the client, and if so, how would you even do that? Or keep them and have a talk about a payment plan? How can she protect herself with a business already struggling due to similar clients?