“... is it a way to get stolen good back circulated into the market?”
I thought if it was definitely stolen, the painting (or whatever).. would be confiscated? I know that occurred with some coins just recently. If the original painting was sold to someone in Maryland and there is no police report... perhaps it was just lost in an estate sale?
Sounds to me like a piece that was quietly stolen from the museum that it was donated to and that it had a sticker from. (Helps to have the sticker for the authentication that would be required in order for it to fetch much in the market.)
With the ‘finder’ not being publicly identified that makes it a little more likely IMO she could be fencing it for someone.