A few things strike me:
1: this is BPD. When needs come up, the focus must pivot to THEIR needs. That's just what often happens... right? Part of the disorder. If your "slice of pie" of "having needs" gets bigger, theirs "must" get smaller, and that's intolerable.
2, and perhaps more important in my eyes: she had a need to be a helpful person (and/or,
a need to feel like a helpful person). When you didn't concur (or find some way of affirming some affirmable aspect) about her helpfulness... you weren't meeting her need for seeing herself/experiencing herself a certain way.
3. all-or-nothing thinking tied to 1 and 2. 1, no shared meeting of needs. Yours or hers -- not both. If yours are being met, then hers "are forgotten". 2, you're either affirming her helpfulness or condemning her as unhelpful (or perhaps an unsupportive spouse). Perhaps that's the condemnation at play for her.
Then she asks if it helped. I said it was interested but didn't address my frustration and that I would like to talk about that.
This is pro level subtle stuff going on here. She is coming across as "with it" and grounded, but it's still her underneath. I too probably would've been lulled by the normalcy into treating her question ("Did it help?") as a normal question... but it wasn't. It was a referendum on her goodness as a helpful/supportive wife.
I'm going to say that the "but" in the statement above was where things took a turn, maybe?
What are your thoughts?
(edit: oops, crossposted with Notwendy, with whom I agree)