My mother, who had an expired Schengen visa from a previous trip in her passport, was just refused entry to the Schengen Area at Frankfurt, from where she was to take a connecting flight to Budapest. It's clear why she was denied entry, I'll explain below. My question is more about the future effects of this.
I live in Hungary, my mom came to visit me here recently and then took a trip to the U.S., planning to return to Hungary before flying back home. Admittedly her own mistake, she didn't notice her Schengen visa was a single entry visa because all her visas from multiple previous visits were multiple entry. As a result she wasn't let into the Schengen Area (on her way back from the U.S.).
Immigration officers indicated that they could see it was a mistake since she had all documents and return tickets and she simply used up her single entry when she came to Budapest first. She wasn't given a special stamp like void or anything like that. I'm just seeking reassurance.
Could this affect her future travel plans?