my 89 year old mother wants to sell her 2002 honda accord lx with 15K miles. (no that is not a typo!) How much can she expect to get? It is in mint condition.

With a 'time capsule' car like that one, you should hold out for the full retail value. An Accord with so few miles should get you more money than the typical ten year old vehicle with much higher miles. It will depend on how long she's willing to wait for a potential buyer that sees the value in this car.