I'm hoping that she'll be able to think what we've said through and come up with her own solution. Work is the obvious answer, although whether she'll be able to get the kind of thing she's used to where she's living I don't know.
Okay, stop right there! This hinting and hoping and your wishy washiness with her, letting her stay for months at a time, letting her move into your home except for sleeping the night in the van, has led her to believe the solution is to convert the garage and live with you, not as a 'fall back' but as the solution to her money problems.
As Black and Amaryllis have pointed out, this is how she functions and sees things.
So you and your H must first have a very serious conversation because if you do this, she will be living with you full-time quite shortly. For good.
She will not think through the way an NT person will and come up with a viable solution. BUT she can get it that living with you and the conversion is not going to happen and once she gets over being angry and upset she might well be willing to engage with some financial planning help.
BUT, you need to be present NO as a united front and your h needs to realise she'll get upset and he needs to be prepared for it and prepared to weather it and not back down.
This is EXTREMELY important in dealing with a person who has ASC. They are capable of getting it. My son will even do this with dinner. 'We're having meatballs'. 'No, I want a steak pie,' cue meltdown. You have to weather it. 'No. It's this or it's nothing' (he loves meatballs, btw, he agreed meatballs on the meal plan) and give him space to process it. Then he comes round and eats his dinner.
'No. We are not converting the garage to an apartment for you. You cannot use us as a place to stay when things don't work out. We are willing to discuss other options and see a financial planner with you, but that one is not an option.'
Keep it simple and be blunt. NO hinting or sometimes or justifications or background.
No to Ireland and moving near her son. I can guarantee the reason she only stayed a month at his and several at yours is because he and his wife have told her NO and been firm about it. If they wanted her around they'd have presented this as an option. They have not and I can guarantee there is a reason for this.
And yes, this is a hill to die on so if you do not want her living with you forever and your home converted you need to make this very clear to your husband.
His desire to help her is admirable, but he's doing her no favours by enabling her. I have to really struggle not to enable my son for an easier life because it's not doing him any favours and I do not want him to turn out like my BIL. I want him to lead his own life as much as possible. He has the intelligence to do this. And he has to learn that other adults are not there to mop up his problems because one day, hopefully, we will die before him as should be the natural order.
She has probably burned through all of the money.
Lodges like this are for rich people to have fun. My sister is very successful now. She has one of these lodges with her family. It's for having some fun holidays and as a bolthole and they don't care if they lose money on it because for them the enjoyment of the property is worth the money. The site fees are staggering but the park has incredible amenities. They've offered it to us to stay in and refuse to take money for this and we've taken them up but have always paid for a professional clean after, left it immaculate, sent them a thank you hamper or tickets to theatre or something we know they enjoy.
You two first need a very serious talk to agree a realistic plan of action and then present it to her because as pointed out, right now she is single-mindedly going to pursue this as she sees it as the only solution.
You have to stop being so passive about this. You really do. NOW whilst you are all relatively young and in good health. Things can change in an instant.