We're going through the same thing with my mom (she's 88). We've been divying up the stuff she needs help with--I handle financial stuff, my sister does medical stuff, etc. The best thing I could recommend is talk to your mom and let her know your concerns, and discuss options if her memory, etc gets worse.
My mom is deathly afraid of ending up in a nursing home--her mom died in one. We've assured her we'll do everything we can to keep her in her house, but if we can't then we have discussed with her moving in with us.
We're in a little different situation where my mom lives in a residential neighborhood with close-knit neighbors who watch out for her and 3 of her 4 kids living within 30 mins, so she's not as isolated.
There may be organizations oriented toward the elderly in you're mom's area--in our area, Goodwill drives elderly to Drs appts, etc, Meals on Wheels delivers food. There may be some organization that would send somebody over periodically to see your mom and make sure everything's OK.
Recommend setting up Power of Attorneys if you have not already done so.