Unable to join crossplatform players

I've had a problem joining my sibling in a game, I am playing on my phone and she is playing on the Nintendo Switch. I've played with her before, I'm unsure as to why I am unable to play with her now. I've tried uninstalling and reinstalling the app, as well as unfriending and refriending her. This doesn't seem to be a problem with other people since she's also playing with her friends. Nothing seems to have fixed the problem, I'd really like a solution since it's frustrating to see my sister and her friends have fun and I don't get to have any fun with them.