The worst enemy of a leftie are other slightly different lefties lol
The good think of federation is that you can mute/block morons. And because there's no "algorithm" you are not shown content that the server thinks you are interested. So you have to be proactive and follow what you want to see, and mute the ones you dislike.
Also, you can have multiple accounts for multiple purposes. It's sane not to discuss politics with other people from other cultures all day, so you can have a dedicated account for that. And other account to have fun in a sane way, which includes muting politics.
In the case of this girl, she was american like the majority of lemmings I believe. But for people from the other hemisphere, the cultural shock may be even worse. My advice for those is always: Just mute. Don't argue and don't feed trolls. Nobody is gonna change opinions anyways.