I told myself the one deal breaker when I finally met someone new was if they had BPD. What are the chances right?

They're pretty high for many here. What happened in your last BPD relationship, and how did it end?
How did you meet your new GF, and how long was it between your last r/s and this one?
She said that she doesn't think the BPD diagnosis is relevant to her anymore and it was the result of a bad reaction to medication all those years ago.
Maybe... .it's pretty tricky work to diagnosis BPD, and if anything, psychiatrists tend to err on the side of caution. It's not uncommon for them to dx bipolar and then work with someone over a period of time to determine if BPD is in play as well, especially because the interpersonal stressors take a while to surface. Her symptoms may not be severe as they were when she was diagnosed, and it's possible that she has coped with fears of abandonment through means that might not be as healthy as long-term treatment.
Do you know if she had any long-term treatment to deal with her BPD diagnosis?
she has identified her anger issues and wants to get help for that.
Do you feel she might be downplaying her BPD issues? Does she know you were in a relationship with someone who had BPD?
So these are good steps
It's always good when someone recognizes they need to work on difficult relationship behaviors

I still can't get past the inner dread that I'm going to accidentally say the wrong thing and set her off.
This part is on you
You can learn how to validate her to increase the chances she won't become emotionally dysregulated. You can also refuse to get on her emotional roller coaster. Someone struggling with BPD/bipolar needs a partner who can stay grounded. You aren't much help to her if you get on the coaster with her.
The way to stay grounded is to have good boundaries. For some, that might mean telling her how you will take care of yourself when being yelled at (e.g. walking away, ending the call, not texting).
Is anyone out there in a long term BPD relationship where they have made it work and are happy?
I think a lot can depend on how severe the symptoms are, and how willing you both are to learn skills.
If she can steam roll over you and get away with being mean to you, it will likely increase shame and jeopardize your relationship success. The key is to have the strength to protect yourself from being abused, to take care of yourself so you have the self esteem and strength to care for her.