UPDATE: I brought the wallet to the police station, I told the cop at the desk the story he was like wtf xD.
Anyway the cop went through it on the desk in front of me so I stayed out of curiosity

.
Apparently she's a Polish student, he found a student card and such. Weird part is the girl had
4 legit visa cards... I don't know about Poland but when here in Belgium to get one you need a credit
check. So maybe she's ultra rich...
SO she could have taken a private jet! And like a private driver or something could have picked her up at the airport.
Which could possibly solve all this
Also some extra info for the guys who didn't understand the time constraint.
I checked Krakow airport, and the earliest departure to Belgium was at 9:30. Which had an estimated time of arival
12 o'clock. She still has to go through pasport control, luggage pickup and all the other crap. Problem is, My mum found it in Brussels... the flight lands in Charleroi... which is a half an hour to 45 minutes distance from Brussels... and hour or so to get to the center... and this judging by car. If she came with the
train... she'd have to take a taxi through the center of town to get a train, wait for the train and get to Brussels.
Easily an hour. If my mum found the wallet on the metro around 13. She'd have to have been in town a while earlier,
for it to get stolen...
EDIT: typo