I'm betting dude, not just because of the stolen photos and being a fan of a very male demographic video game, but mostly because of her unwillingness to use a mic. Even if she was an ugly girl, no one could tell how she looks by her voice, so why not do it? She could have kept this scam going and gotten more simps by just talking on the mic, even doing it just a handful of times would have been enough. Unless she's a woman that smokes 10 packs a day and sounds like a grandma, it would be stupid for a woman to opt out of something so simple that would give her scam more credibility.
Now the question is, is it a troon or just a regular male scammer? I remember back in the day, even as kids, me and my brothers learned that you can get a bunch of free shit by playing as a female character or by claiming to be a girl. You didn't even have to do anything or work hard, desperate guys just start throwing money and items at you. This meant that lots of guys had two accounts, one female to get free shit, and then their main account, where they would use the free shit. It would explain why Mandy has no other TF2 community presence despite being apparently such a huge fan of the game; that account is just for scamming, her main account is elsewhere.
That said, I could also believe this is a troon.
Whatever it turns out to be, it still baffles the mind that Nick went ape shit over potato quality photos and it's funny to think of him fighting with his wife over someone who isn't even real.