Hi. I am sorry this happened and brought up so many emotions for you. I do think that is normal to have happen. You will still have feelings even after a break up. Unfortunately with things till fresh, time has not had the chance to do the dulling it usually gives us.
If your question is if it is normal for her to seem like a deer in the headlight, I can't say. I do think it is common for anyone when they are caught unawares. I think in a pwBPD (person with BPD) it may be common because they get overwhelmed by their emotions, just like us, but are less well equipped to handle them in a mature way.
it triggered all these feelings I was trying to let go, and so hurt that my existence or my kids were not even acknowledged
Yes, it is hurtful when this sort of thing happens. Give yourself time. Same with your daughter. She will follow your lead in how you choose to handle such things so be careful there. One thing to remember is that it is rare that any reaction the pwBPD has anything do do with us. When their emotions are engaged like that, they can really even see us. So try not to take it as a commentary on you and your daughter.
hang in there.