Another person with BPD here, and this is absolutely spot on. This will only get worse if left untreated. Enabling her is only going to hurt both of you in the long run.

If she absolutely refuses to get help, you need to leave. However if you give her the ultimatum she will (hopefully) seek help, as people with BPD will often do anything they can to avoid abandonment. This is how I ended up eventually seeking help, my ex left me due to my outbursts whenever I had an episode.

If she instead threatens suicide, call the police. It might seem harsh but borderlines sometimes need to see the seriousness of their outbursts. I'd also consider posting/lurking r/BPD because they are very helpful with these sorts of situations.