What state does she live in? Depending on where she lives, low income seniors can receive financial assistance for energy usage, and many states (like New York) provide free AC units to qualifying seniors. Check out this link: http://www.needhelppayingbills.com/html/cooling_bill_assistance_progra.html
Your county social services should be called to go and check on her. It's so sad when they can no longer maintain a home. It would be much safer for her to move to a senior apartment where all the maintenance is taken care of.
and this one: http://www.benefits.gov/benefits/browse-by-category/category/ENA