I had a friend in a similar circumstance (JW, btw). It got to the point that she was very close to divorce - talked to her pastor and everything.

Turns out her DH was depressed and has ADD. The spending is self-esteem related. It's a vicious circle - spend, feel guilty about it, get depressed, spend to make it feel better, etc.

Chronic spending is also common in people with bipolar.

The thing that fixed it was him getting a decent job, which improved his self-seteem. They sold all the big items he kept buying, like motorbikes, car etc, she took control of the budget and access to the cash. They moved to a cheaper area as well.

You've mentioned she's a martyr to this. She needs counselling herself, or she'll just end up behaving like a victim. Make sure you're not enabling her rather than supporting her. Rescuing people who want to be seen as a victim doesn't encourage them to pick themselves up and get on with things. Give her links to resources that will help but stop bailing them out.