I wish I had some helpful advice to give to get your mum out of that situation but I really haven't got a clue.Sunk Cost fallacy. "I've already put so much time/money/effort into it, might as well see it to the end!"
And that's what I'm worried about. She hasn't spent tons of money specifically, but the amount of time and attachment she has... if money gets brought up then she's all in, because why wouldn't she be? She's already invested hours and hours of online interaction with them. She's part of the "family", you wouldn't betray your "family" by not supporting them. Ugh.
My mum is trouble for similar reasons but different circumstances and these days I'm just disinterested. She doesn't want help so I just leave her to it.