Looking for advice on mother's deteriorating mental health

Hey, I dunno if this is an appropriate place for this, and feel free to take it down if it's too direct/off-topic or what have you. I can't post this on reddit because my mom browses reddit and it would be painfully obvious.

So, as some of you may know, Backpage was a website like craigslist that got shut down completely due to complaints/reports of trafficking. In that shutdown, many people lost their jobs, my mother being one of them. My mom received a severance pay, and had to find work. Within that same timeframe, she also broke things off with a man whom she had been dating prior for reasons I still don't know. After having to sell her house, she tried to make it on her own, but then inevitably had to come and live with me and my Dad (Whom she had divorced about 10 years prior)). At some point a year or so ago, she had a nasty fall and hit her head, concussing her. Lately, she seems to be coming unhinged.

Her behavior started with her continually retroactively accusing my father of cheating on her ~15 years ago on several occasions based off of information she swears happened but cannot corroborate. She has, in recent memory, been known to make false claims and, when presented with proof refuting her claims, to discard said proof and continue to push her claims instead. She has tried to get me to "remember" incidents over 10 years ago where she ran across "women who were his type". On top of that, she has accused my father of going into businesses she has applied for and telling them not to hire her. My dad wants nothing more than for her to get back up on her feet and get going. I have no idea why she would believe this.

We had another incident where my little sister went downstairs to get something to eat, and used the microwave to prepare it. My mother interjected and told Ali that she shouldn't be using the microwave because she's afraid of the radiation it gives off. My little sister politely told her that that was bullshit and that she isn't worried. My mother then grew angry, told her something along the lines of "Fine, I'm not going to care if you die then", took her phone, and sent her upstairs (We all shave our rooms upstairs and she has her space downstairs, where the guest room is). This isn't the first time she's posited a completely ridiculous and baseless claim/conspiracy/concern, however I hadn't tried to refute it before.

I texted my Aunt and debriefed her, and she said that she was aware of my mother's mental health declining, and she wanted to help, but I guess she said something my mom didn't like, because my mom has since blocked her on her phone, severing the only means of communication between them (She's 2 states away). My mom seems to keep doing this to people; saying and believing untrue/ridiculous things and becoming increasingly angry and hateful when she is refuted or called out on it. She has severed ties with her Aunt, the sister of my deceased grandmother, who tried to tell her she was wrong after accusing my grandmother of various things she didn't do. She doesn't have any family left that she hasn't pissed off.

The only person left in my house who she isn't angry at is me, but I am supremely bad at handling these things and would much rather retreat into my room and not come out until it's all over. My girlfriend living with me is trying to provide support as well. This morning, my mother asked me to drop her off at a homeless shelter. She has a bed, food, clothes, a shower and restroom, and WiFi here, but she feels so much that my father is the root of all of her problems that she wants to leave at any cost.

I don't know what to do now that my mother is slowly and surely losing her goddamn mind and is driving out everyone who loves her when they don't reaffirm her insane delusions and accusations. It hurts to see my father struggling to do something, because he can't just kick out the mother of his children; he still loves the woman he married. We can't tell her she needs to seek help, because that is interpreted as an insult and calling her crazy. I've tried, again and again, to tell her that we are all here to help her and we want the best for her but she seems to discard every good thing I say and pick out the worst, even if I didn't intend any kind of negativity. She's getting to the point where she's beginning to lose her temper with me and I'm afraid that that will be the final nail in the coffin. My father tried calling some place (I believe they specialized in mentally unwell people) and asking for advice, but when he asked them to call my mother and they agreed, my mother got angry at them and accused them of "collecting evidence" for my father. It's out of their hands if she isn't harming herself or others.

I don't really know what I expect from posting this. Maybe commiseration, maybe sympathy, or advice, but I'm going fucking insane and do not have any prior experience to help me cope with/fix this and I would really appreciate if anybody does and they're willing to share