The voucher is normally set up by EK FRA, but I always had to collect it from the Airport Desk at MUC before starting the trip. I have tried various reasonings, but EK FRA was always firm. I suggest you ask if you can pick up the voucher for your GF ahead of time from the MUC or FRA airport counters.

Normally the Airport staff pulls up your reservation, takes a good look at the details and then starts the process of issuing an MCO and charging your credit card manually.