That's hilarious. I used to work as a senior backend developer in one of Berlin's startups. Another senior BE dev was a native Russian speaker, so despite our fluency in English we started chatting in Russian now and then. Our conversations were meaningful and respectful (unlike those held by our predominantly Italian sales team who would shout out words like "cazzo"). We didn't mean to exclude anyone either, we only…
If she felt like the right choice was to bring it up with management, it would seem fairly clear that she felt you were speaking Russian often enough that it would be an imposition to communicate with you, in a way that's quite common in Berlin and in Berlin startups. Though obviously not as much as German, it would be the common crossover language.
If you're senior and they're junior, part of your job is mentorship, and you should be making it as easy as possible to consult with more experienced people if necessary.
Those are the general principles I've always followed, and would do so regardless of whether they seemed incompetent or not. You need to be able to set your ego aside.