I would imagine that her father or grandfather probably served in World War II and brought that home with him as a souvenir.
I know that when I was a kid, maybe seven or eight, my uncle brought me a pineapple grenade as a souvenir. The explosives and the detonator had been removed, but otherwise it was real enough.
Big deal. The whole country is going to the dogs, Muslim gangs are running amok, burglars are getting suspended sentences, and these jerks have nothing better to do than to use hydraulic rams to break down the door and arrest a 13 year old for having an old family souvenir in her closet.
When I was young an uncle gave me a M1 rifle he had the barrel was lead filled but I used to play war with my friends with it the rifle was heavy but looked cool carrying it around.