IMO it would be best to ask an experienced tax adviser.
Is your girlfriend a Belgium resident, e.g. is she spending more than 6 months in a year in Belgium? If so, she will be entitled to pay taxes in Belgium to the Serbian transfers.
If she's a Serbian resident, it could go without issues for low 5 digits. For the higher amount, it's almost certain that the bank would require AML proofs as trading transactions, etc.
I would take this advise instead yet not all people who do respond will actually be having those valid points that should really be followed.
If its still in doubt then better to seek for professional help would be the best option.So that you would really be aware in regards to the possibilities of problems that can be faced
off when making such transaction.
Its just impossible to think that there would be no questions asked even if it isnt taxed or whatsoever.When banks do notice those big transfers then
expect that there would be some sort of questions on where those funds came from.