As a kid we used to say, ‘finders keepers, losers weepers’. In this case though keeping the gun could possibly result in a big can of unwanted worms. Reporting the gun to police could possibly lead to solving a crime(s).
I would have been compelled as a good civic minded citizen, to do exactly what my daughter did and turn the gun in.
Liking my Glock as I do, for purely self defensive purposes, I would have regretted turning in the found weapon if it was in very good condition. However, I do not need a self inflicted can of worms. Life has enough already.