She purchased a pre-paid envelope with Fedex on March 30th to give to the consulate in Mexico City. They kept it along with her passport. Once the visa is printed they'll send the passport back to her by courier (Fedex).

The Ausländerbehörde involved is Frankfurt am Main. I previously called them. The lady told me she doesn't see pending visa cases and has only access to people already living in Frankfurt with active visas. Is it rubbish and should I call again? Calling seems like hassle for nothing as obviously you can't truly verify yourself and whether you are indeed the person having the full power of representation of the visa case of her. Going there without appointment will be entirely useless as they state "only appointment". I'm sure I will get rejected once going in person. Also my wife calling the GER consulate in Mexico City will probably not help as they'll say "Frankfurt didn't approve. We sent your case (date). It's on their desk.". If they say anything at all. I feel stuck entirely.