Do you know how to use ITA Matrix (
http://matrix.itasoftware.com/)? It can be tricky, but I think one of the better free search engines for flights. Google flights and Kayak also good.
I'm about your mom's age, so qualified to comment on flight needs.
If she can lift it and lug it, carry-on luggage saves the risk of breakage, loss and waiting for it at the other end. Odds are good the first two in the list won't happen, but she will be impatient to get out of the airport and see those babies.
Avoid the last flight of the day. If something happens to that one, she is stuck until the next morning.
Step up from the absolute cheapest flight where you don't get to pick seats. Find her flights where she can be on the aisle and well forward. The aisle lets her get up and walk mid-flight (helps prevent blood clots). Lets her take a bathroom trip without disturbing seat mates. Well forward lets her off the plane sooner.
I don't see any non-stop flights, even via Chattanooga and Pensacola. Maybe somebody that flies in that general area is aware of something ??
You don't mention travel dates, but it would be good to stay away from the heavily traveled Christmas rush.