There are no plans for the society to assist older ones who have got into financial difficulties because they made no provision for their retirement. I think the legal bods thought this might come up and I am sure I saw in the magazines that people should plan for retirement whilst hoping the system ends soon. Oh and don't forget to leave money to the society in your will.
The societies approach has always been to say to those in difficulty "keep warm and well fed."
I suggest where possible your husband is the one who approaches the topic with his mother, otherwise you are the evil one, she needs to know that you both feel the same way and there is no emotional leverage.
If your mum in law is fit it may be worth your husband suggesting that since her circumstances have changed she needs to be more proactive about finding a part time job rather than pioneering. She may genuinely be unaware of the cost of living and the financial strain she is placing on the household. Show her how much you have to pay out each month for amenities etc divide by people in the house and show her how much a meaningful contribution would be. She may be quite shocked to discover how expensive things are. Even Paul supported himself whilst pioneering because he appreciated that he couldn't be a pioneer and a financial burden on others.
I feel for her she was expecting to see a reward for all her hard work and instead she is in dire straights but she is still to a certain extent living in a fantasy world. In your household everyone contributes financially so she needs to be prepared to do so as well if she wishes to remain with you both. Be supportive about assisting with CVs etc but if you are serious you need to be firm.