Using the wrong gender or articles quickly gives a hint that you are some lowly educated factory worker living in Germany for 20 years and not caring to learn the language.
A lot of Germans are to varying degrees prejudiced against foreigners, especially if you're brown or can be read as Turkish/Arabic or Eastern European. If you pass as white European you're more likely to be read as educated but still learning the language whereas otherwise your language problems are more likely to be attributed to a general lack of intelligence and education.
I'm not saying all Germans think this but there are certain cultural clichés around uneducated "southerners" (generally Italy, Greece, Turkey but also Arabs and everything West of France) and Eastern Europeans speaking broken German the same way Americans have stereotypes about people speaking AAVE.
In other words broken German has a cultural stigma but depending on how you are read you may be less impacted by it. If your career is going to involve speaking German a lot, it's probably advantageous to speak it well.
It's the general bad practice of putting individuals into larger groups with a stigma based on visual appearance.
I think a lot of the resentment about bad German skills in my generation (80s/90s) comes from 10+ year residents and 2nd generation immigrants not capable of speaking our language correctly.
There are reasons of course, just sayin'.
Doing so while not allowing them is cruel and stupid like punching someone for having a black eye and justifying it with their face looking weird.
There is the option to leave the country.
It doesn't sound entirely unreasonable or unfair to me.
We also had a lot of highly educated migrants from Yugoslavia back in the seventies and they were appreciated back then. But after the Balkan wars they were suddenly the bad guys despite some of them being perfectly integrated in our society and sometimes being the third generation to live here.
It's funny how fast the perception shifts and how quickly we are to judge on the prejudices we have of a group of people and not on the individual.
"Hedonistic lazy people with dark hair who steal our daughters" seems to be the general idea. This is somewhat distinct from "lazy people with light hair who steal our things", which seems to be the stereotype against Eastern Europeans.
Eastern Europeans are very much white. Their accent might give them away but certainly not the skin complexion.
My aunt, an American who has lived in German-speaking countries for 10+ years and can say almost everything she'd want to tells me she still gets treated less seriously because of subtle mistakes like that in her speech.
It may help your Aunt to learn German (again) with beginners books. There are good self-learner books with interesting exercises. They are less than 20€ per level and if you are already good, it should be easy to do multiple pages per hour.
It would be important for a native speaker to check the answers, though. And also the solutions should be crosschecked with the books solutions, if there are any, because many Germans don't know all the rules correctly. If in doubt, just stick with the book.
Probably it's good to know that it doesn't matter, just so that you feel less fearful and tend to speak more, even wrong....
Native German speaker here: I disagree with all the sentiment of "less fear". Better concentrate on your ability to formulate grammatically correct sentences.
In school, I often felt that the German grammar works somewhat like a mathematical proof system (and asked myself why German grammar is not part of math classes). When studying mathematics, you first have to learn to write correct proofs. It makes no sense to try learn something more deep in mathematics if you have difficulties writing elementary proofs.
For German, it is the same: first learn the internal structure (grammar) of the language (just like predicate logic in mathematics) and just like thinking how to express something that you want to prove in predicate logic, find out how to formulate something in German's grammatical structure.
Only after this elementary step, you can begin with more complicated things.