My (22F) mom (50sF) believes our family is involved with Nazis and that our house is bugged with recording devices.

My mom fully believes that my family members are secretly involved with Nazis, that my dad is having an affair, that our house is bugged with cameras and microphones, and that my extended family earns their success by doing crazy shady stuff (she has insinuated by killing people or stealing). She?s been dealing with these thoughts for 5+ years, but I was only made aware of the true extent today.
She fully broke down today, hysterically crying to the point where she could barely talk. I've never seen her breakdown like this before. I tried to comfort her, but I didn't know what to say to make her feel better. There?s no point in giving her the facts. The few times I?ve tried, she says "you don't really know what's happening, you're biased" etc.
Before today, I thought her only delusion was that my dad was cheating on her. Clearly her delusions go way beyond this.
As you can imagine my parents? marriage is on thin ice. My dad is tired of being accused of doing horrible things. He is a hard working guy who loves his family. We are not a perfect family by any means. We have the usual **** going on- some extended family passed from cancer, some are going through divorce. But nothing crazy. Nobody is involved in anything shady. My mom is miserable about a situation that isn't even happening.
After her breakdown I finally convinced her to start therapy. I already set her up with an appointment. But everything I?ve read about paranoia says how slow the progress will be. Patients often believe their therapist is out to get them, and my mom is no different. She thinks that someone will be tapping the phone line or recording the video sessions (since she can?t meet the therapist in-person due to Covid). I?m afraid if she needs medication, she?ll refuse to take it.
I?m posting in the hope that someone might relate to my situation. It?s frustrating and disheartening for me to hear what she thinks about our family (my dad especially), but I?m afraid if I set up boundaries from her talking to me about this, she won?t have an outlet to talk about it. I don?t want to encourage her delusions by saying ?I believe you,? so all I do is sit quietly with her. It?s been really hard lately because I?m quarantined at home and I?m the only person she talks to about any of this (everyone else is out to get her). I had to sneak around the house today to make calls to psychologists and our insurance company because she doesn't want my dad to know about it. I love my mom more than anything and it breaks my heart in a million pieces to see her like this.
Side note- my mom is very high functioning and rarely lets it show when she's freaking out (except around me). When my dad and brother are home, everything appears normal.
TL;DR: My mom is suffering with intense paranoia and believes our family and friends are involved in crazy shady stuff and are out to get her. It?s gotten to the point where she cries about it every day. I?ve already set her up with a psychologist, but what can I do to support her?


Source.