Monk,
Your partner is certainly more self-aware than my husband, but that is probably because of the 5 years of therapy she's had. My undiagnosed husband would never dream of apologizing for his behavior (which sounds pretty much identical to your partner's) and only wonders why I don't just get over it.
Her awareness is HUGE. Her initial response is to blame you for whatever bad happened (a BPD behavior for sure) but then she knows that wasn't the truth when she comes back to her own mind. And it is like they're somebody else in those rages/tantrums which is a part of the dissociative aspect of the disorder. Here's a fascinating discussion about
BPD BEHAVIORS:Dissociation and Dysphoria that should shed some light on what's going on during those rages.
Your relationship has something that most of us in relationship with someone suffering from BPD don't have, that awareness and recognition of "the truth of the matter" once she has passed through the rage. And since she is the one who is learning how to behave differently (recognition being on the road to cutting off the behavior when it starts) you will probably have more success in building some boundaries to protect how you want to be treated. Those will highlight to her your intentions for the relationship. This is awesome!
Boundaries can certainly be made in love and kindness, they are simply an action on your part to show how you will and won't be treated. This is a great article and workshop on the subject of boundaries that can help you figure out where you want to start, my first boundary was about my valuing Respect in my relationship:
BOUNDARIES: Upholding our values and independenceLet me know what you think! I learned so much from it, but you may be farther along than I was. (I think our dogs were farther along in establishing boundaries than I was!

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