You geniuses do realize that she might be playing on a PS4, don't you? You can see her PS4 Pro on the very first page.
Hard to find a console FPS that supports keyboard and mouse, if you ask me...
And yes, you can actually play modern consoles on PC screens. My PS4 is hooked to one of the screens my PC uses.
As for why she'd play an FPS on a console: because she wants to.
Seriously, people, it's a game, and games are made to be enjoyed.
If you enjoy playing FPS on a console more than on a PC, why not? No need to make such a drama. It's her choice what she play on what platform, deal with it.
Let's leave the master-peasant flame war where it belongs (YouTube, for instance), okay?