I deal with depression, schizophrenia and borderline personality disorder as well. She should see a doctor and a psychiatrist for sure. However, I will say I can understand her dislike of people.
I absolutely hate people and I tend to stick close to my boyfriend and when I'm with him I tend to stay in his room most of the time. People scare me and judge the moment they know I've got any sort of mental health issue, so I like to stay away from them. It could be the same with her as well, although that's no excuse to be rude and hate on people (especially online, that's petty tbh). I'm not certain, don't completely base your opinion off me, but usually I get irritable and lash out in situations where I'm more scared and terrified than anything. I dislike my boyfriend's friends as well, but it's not just because I dislike people in general. Their habits remind me of people and the messed up morals that led to me being hurt in the past. It could be the same with her (reminder, you should always openly communicate with your lovers about such things. Communication is key. Support and comfort is key.)
I also think that disliking people isn't a bad thing as long as you aren't completely closed off to everyone and you aren't a rude and spiteful person. If you're polite and nice but just avoid people altogether I think it's fine. So, if you could, I would suggest being supportive and understanding of the fact that people are actually really scary to those of us who've been hurt in the past and people legitimately are really really awful a lot of the times. People are terrible, and those of us with mental illnesses like this can be terrified or hateful because we've been hurt and betrayed so many times and judged by others. Try to defend her decision to stay in the room and help her feel safe and comfortable wherever she is. Don't pressure her into situations around people she's not comfortable with. Those sorts of situations can legitimately be overwhelming and terrifying. If absolutely necessary, hanging out and getting used to one person at a time could be alright. You'd have to be there with her, in a space she's comfortable in, and maybe work on hanging out with one singular friend or family member at a time to let her get used to them and get to know them without overwhelming her with so many people at once.
But don't just let her walk all over everyone and be rude either. You should (gently) let her know that it's not okay to be rude and impolite even if people are awful. "Do no harm, but take no sh*t." Terrible people aren't even worth the time to get upset and angry over, so why bother even giving them a second glance? Just ignore them and move on. Try to be polite and nice and if someone does turn out to be terrible then just drop 'em and be done. No drama or hateful remarks, all that just makes things worse.