She got greedy. Back when a buddy and I administered our SWIFT platform there were a couple of well publicized exploits of the system for millions. We discussed how easy it would be to write a script to randomly skim a fraction of a cent off of transactions over a long period of time, just don’t get greedy. No one cares about rounding errors.
If this lady stuck to random fillups for free once every couple of months she probably could have flew under the radar for years and more importantly had a better claim to ignorance if caught.