I'm worried about my best friend

Hi, everyone! Before I start I want to say English is not my native language, so if I make any mistakes, sorry about that!

Anyways, I'm in need of advice because lately I've been very worried about my best friend! She's always been quite hot-headed and snappish but in the past few months she has been treating her boyfriend in a downright mean way. They've been together for about a year and they've always had lots of fights but now more so than ever. She will literally get mad at him for nothing. For example, recently the three of us were watching Breaking Bad which he says he has seen 3 times and this is the fourth time he'll be watching it. At one point he asked something along the lines of "When did this happen?" and my best friend got mad and told him that he must be lying about having seen the show three times already because "if [she] had watched it that many times [she] would have memorised the whole script already!". He then asked why she was getting mad at him for no reason (in a neutral tone, btw) and she started yelling that she was getting mad at his lies and then she got up and said she was leaving. He started apologizing immediately and trying to make her stay and she finally did it but was still obviously angry. And I wouldn't describe her as a person who values honesty all that much. Actually, the three of us are kinda sorta pathological liars. I can't think of anymore examples right now but it's always ridiculous stuff like that that she gets mad about. She never does this with me but I guess I should mention that I'm somewhat of a doormat and I hate conflict so I always try to avoid it at any cost by agreeing with her about everything. He's very similar to me, personality-wise but he still at least tries to stand up for himself every once in a while. Most of the time she starts yelling at him about such stupid things that I'm convinced she's just entertaining herself by watching him suffer (she's literally sadistic but that is a quality of hers that both me and him usually find charming). Sometimes when she's having a fight with him she'll smile at me when he's not looking. But other times she'll roll her eyes, as if telling me that she thinks he's an idiot. It could be that she wants him to try to apologize to her by hugging her since he does that a lot but most of the time she'll yell at him for that, too, screaming "Don't touch me!". So I just don't know.

Another thing is that she has ZERO social anxiety and she's been singing on stage since she was three years old and has never had stage fright. For the past several months, though, or maybe the whole year, I'm not sure, she's been having some issues with her whole body and her voice shaking when she goes on stage and she keeps saying she's not nervous but she has started taking valerian (or is it called valium in English?), even in her everyday life, not just when she's about to perform. She's had low blood pressure problems since she was 12, I think, but it might have been getting worse lately. She also says her heart sometimes beats faster and that the valerian is going to help but in her boyfriend's opinion this (the low blood pressure and faster heart rate) has been been happening BECAUSE of the valerian. She's also been smoking weed roughly three times a week, although she stopped at one point for a month and a half, for the past two years since she was 14. Both her mother and her grandma from her dad's side of the family have schizophrenia and I've read that weed might trigger this for you if you're under risk.

Also, about a month ago she told me that her whole life she's been "on autopilot". She said she never thinks, she just does thinks impulsively. This is very evident in my opinion, both in the way she acts and especially in the way she talks. When we first met I legitemately thought she had some sort of mental disorder. She has the wackiest (and funniest) sense of humour I've ever seen and she constantly says things that don't make sense or don't even form a coherent sentence. She has been like this way, way before she started smoking weed. She can sometimes speak in a relatively normal way when she knows I want us to have a serious conversation but it doesn't come naturally to her. I'll just give one example of a nonsensical thing she said yesterday. Her boyfriend hugged her and she just stood there and he asked "Aren't you gonna hug me back?" and she said, in a surprised tone "And a shipwreck, yes.". He usually ignores her, I laugh my butt off and that's that. But maybe it's a sign she might have some problem? I really don't know what to think at this point. About a year and a half ago she was diagnosed with a hormone imbalance - she had too much estrogen - but as far as I'm aware they took care of that.

So she could have a physical problem, she might have a mental problem, I don't know. I'm just worried about her and I don't know what to do. I don't think she'd agree to seeing a therapist or something like that because she says she doesn't like how they put labels on everybody. How could I help her? What questions should I ask her to maybe get more information about her mental state? I'm just worried and I want to help if I can.