My Girlfriend Is Mentally Losing Herself, She Had A Lot

my girlfriend is mentally losing herself, she had a lot of past trans in her life. She has I’d call advanced insecurities. For example this girl I grew up with she thinks I’ve been seeing her while we’re dating and I’ve not seen her in 10 years. It’s went from tgat to she thinks this girl is breaking into her home and stealing her things. Stealing her mattress, kids toys pots and pans. Things no one would do. But in her mind this is happening. She also thinks I’m behind it all. I’m all she has around here and although she blames me a part of her knows she’s safe with me. She thinks others are out to get her now. She was never like this other than her normal insecurities. I think she’s just built up these things she now believes in her mind and I don’t know how you convince someone in her state to get help before it really gets bad. I’m looking for advice on how to handle this, thank you