She should not return the money even if she knew where she got it. If someone sells something that means so little to them about their family that they wouldn't know about Grandma and how she stored her extra cash and the hard times they once had...they deserve to lose it! My mom used to tuck bills here and there and when she died I went through her little purses and found maybe a twenty or so. But it was the memory of her that mattered and I was very careful about letting her things go.
When my mom died, we were cleaning out her garage for a weekend sale. Well, my older brother and I decided to play catch with this old metal vase. My sister-in-law took it after we had dropped it 'alot' of times and she was going to practice tole painting on it. When she got it home, she looked closely at it and it was pure silver. Needless to say, my brother and I are still in the dog house over this one. So the moral of the story, be careful with our parents 'junk'.
If I was to decide to hide money, I wouldn't be telling people where it was hidden. Kind of defeats the purpose.
My parents grew up during the Depression, and tho dad never hid money, my mom hid money everywhere...in her little change purses, in the pockets of clothes hanging in the closet, in between the linens in the linen cupboard, in her shoes, anyplace she could think of...
When she got old, she got Alzheimers....but she still liked having money she could 'play' with and hide...so since she was living with me, and in my house, I would always just hand her a few bills, and let her go at it...she would disappear a few minutes later, without the money, and she could never remember where she put it... but she was so happy with her little cache of hidden money, even if she could not remember where she put it...
After she died, we went through most of her things...gads, nothing like having $1, 5$, $10, and $20 bills flying out at me, from all her little hiding places....I figure she was happy playing with and hiding her money, for it kept her smiling and busy, and years later, I had a nice little accumulation of money...