Thank you for sharing this with us. This is a really complex situation. I'm sure it must be very hard for you to see your partner during these episodes, dealing with the fact that she has little trust in you when it comes to loyalty. It is never okay to endure abuse from your partner.
I think it's really amazing that you want to help her, and it really sounds like she needs professional help. It's important for you to realise that you can provide as much evidence as you want, but bottom line this goes beyond her ability to be rational, these are unfounded delusions that she truly believes. From the stress and betrayal that she has gone through, it sounds like these things have piled up overtime and her mental health it suffering.
Have you brought up the idea of therapy with your partner when she isn't having an episode? What are her thoughts around it? How does she respond to you when you tell her how worried you are? When you manage to calm her down, what does she say and how does she react afterwards?
I can understand where your friend is coming from. Having to endure daily abuse from your partner for whatever reason is extremely unhealthy. This is not a reflection of yourself, and I'm sure your partner is a good person, however sadly mental health issues can warp our feelings and behaviours very negatively. I think it's important for you to know that you can be there to support your partner, but she needs to take the steps to get better in order for your relationship to continue.
Does your partner know how this is affecting you? How does she respond? Perhaps if she realises the affect on you, she will be more willing to take the steps to do couples counselling, or perhaps make the decision to seek professional help for herself.
I think it's amazing that you want to help and support her, and I want to remind you that your health is extremely important in the process. It can be easy to pick up all the weight for your partner to get better, but in the end it's up to her. I really hope that she takes the steps she needs to get better, and that both of you can move forward in your relationship. As amazing as your partner may be, you shouldn't have to endure abuse just because she's unwell.