I’m surprised to hear that you have to have a Kazakh card to pay through ePay, in my memory it could be an international one too.
Back before ePay existed and when I had to pay for a non immigrant visa fee, I had to physically go to the closest Halyk bank (which the ePay system belongs to and the bank the US consulate uses to collect fees from applicants) office and paid my fee there after which it took several hours to “clear” on UStravedocs. My initial thought is to go a Halyk bank branch and present this to them, they might be able to help
I do hope @HashWad comes back to tell us how MIL was able to pay