Posted By:
peter chaoBill,
It's true that the old lady may know that the cards are valuable, but certainly she doesn't know they are worth approximately $250 each.
If she needs the money, the consignment to an auction house is a good idea. Then divide the money.
If she doesn't need the money, show her a price guide and either make her an offer or divide up the cards in an agreeable manner.
You are doing the right thing and sometimes that's hard to do. 
Peter C.