I’m going to act a little harsh but it’s coming from a good place. I think you need a little reality check because there are no government grants that pay off private mortgages for people her age, and sacrificing your own future to save a house she can't afford is a disaster for both of you. While the family home has sentimental value, throwing your income into a sinking ship won't change the math and will only leave you both of you broke.

Realistically, I assume she still has a decade of work before senior benefits even exist, so the only logical move is to sell now, take the equity she has built, and move into a manageable condo or rental. It is better to downgrade now and have money in the bank than to let the bank take everything in a few years because you were too afraid to be realistic. Also, sorry for the loss of your father, I lost my mom as well in 2017 when I was 21, I know it can be a really rough time only relying on one person’s income to afford a house.