You will have to pay the KLM change fee. Sorry. I think it stinks too but I think you would have trouble getting a refund for the flight even if your girlfriend had died. You almost never get a refund for a medical problem, that's why everybody flies around the world spreading the flu, so that won't work either. Almost nothing works. You will have to pay the fee or fly the original dates. If you find a workaround, please post it here and let us know, because we would all want to be able to learn the secret.

Airlines don't make money moving people around the planet. That's the part of the business where they LOSE money. They make money from fees. That's why they have no real way to get away from the fees, other than death itself -- a bit drastic.