Since you found a flight that costs about the same as driving, definitely take the flight! The drive from TN is long and tedious. Make sure that you sign up for Disney's Magical Express to transfer from the Orlando Airport to WDW.
There are some caveats there. I don't know which airport the OP's party would be leaving from, but they should find out if it's a nonstop flight or not. Even a 1-stop flight can make the trip more than 4 hours, plus the time it takes you to get to the airport, PLUS the time it'll take you to park your cr at the airport if you have to drive, PLUS you have to get to the airport 2 hours before your flight for the fun-filled security probe, PLUS however long it takes to get to Disney itself from Orlando Airport. If all goes well - you get a ride to the airport, it's a nonstop flight, you get right on a Disney's Magical Express bus - that could be around 6 hours. If it's a connecting flight, maybe an extra 2 hours on top of that, so 8 hours total.
I don't know where in TN the original poster hails, or how close he/she is to an airport. I had family that used to live in Rockwood for a few years. From there, a drive to WDW is under 11 hours if you drive more or less nonstop.
So from there, you can decide whether or not the drive (so you have the choice of using your own car to get to the parks) versus flying (and relying on Disney transportation). Now if the difference in time is 5 hours each way, that's more tempting to choose to fly than if it's 3 hours...
But also consider this - unless the OP or his/her mom has to go to work the very next morning that they return from their trip, they can leave WDW whenever they want on their departure day, IF they have their car. They can close the joint if they want, take advantage of EMH if they want. You can't do that flying, you're expected to be back at your resort to be picked up...what is it, three hours before your flight? And if the reason the flight is cheap is because the returning flight is earlier in the day, your entire last day at WDW is relegated to a couple of hours, if that.
Finally, if the OP and his/her mom intends to visit other resorts for meal or just to be looky-loos, they are potentially waiting for 2 modes of transportation each way. If they want dinner at Boma, it's a bus ride to AK or one of the other parks, plus a bus ride to AKL. Whispering Canyon Cafe, a bus ride to MK followed by a bus or boat to WL. Times like that, it's much more convenient to have a car.
Just throwing all that out there. The TOTAL time of flying (not just the flights but getting to/from airports and the wait time) and whether or not they're nonstop flights, AND whether or not they plan on visiting other resorts, can play a deciding factor in whether or not driving is or is not "worth it." Now, we tend to drive anyway, and we live in NJ. But going from Tennessee, it'd be a no-brainer for us to drive. Leave the house when we want, stop when we want (IF we want), no worries about setting off security scanners, no having to sit next to a Tuberculosis Tommy on the flight, be able to visit the other resorts whenever we want without worrying about extra buses, and being able to stay as late as we want on our last day is more than worth the extra couple of hours in the car.
EDIT - based on the pic on the OP's profile, I'm guessing she's a she, so sorry for all the gender-neutral stuff before.