It sounds to me as though renting out a house which is not in the best location (makes it difficult to find good tenants) and is not in the best condition (also makes it difficult to find good tenants, and will mean constant input of time, money and expertise in repairs and maintenance) would be a bad idea for anyone other than an experienced, professional landlord. I mean, I've got two rentals and have been renting property out for 6 years, and I wouldn't take that on: even if I put money into getting it into good repair there's nothing I could do to change the location.
If your mother sells, she will get 1) any equity she has built up, 2) away from the need to put money and effort into repairs and the burden of it's ongoing maintenance, 3) the freedom to chose where (and with whom) she lives. I don't get why any of that should be a "waste", particularly if that's what she wants.
There is no way in which your mother can get full value for the property unless someone pays her full value. You can get the property for free only if your mother dies and leaves it to you: please don't take this as a suggestion that you should kill her and forge a will in your favour.
I don't know what your situation is, other than that you live with your mother. But if you are of an age and ability to work, then you should be working your way to improving your financial situation rather than wishing for someone else to give you something for nothing.