Pretty sure a non B business visa is the way to go, or you could ditch the Mrs and and marry a hot Thai chick as that's a much easier and less stressful visa to have 🤣
having lived here 8 years you always have to be on your guard I always count my change before whenever I pay for anything of if I take money from the branch, can't trust anyone here lol
the only things it could possibly be then could be fee for overseas transaction or currency conversion but surely that would be stated on the remittance slip when she took out the money.
Other than that the other two options are that she has be accidently short changed or the person dealing with it stole it (this is obviously if it was withdrawn in branch and not atm)
Cant really think of anything else that it could be 🤷