I completely agree with P.F.Change, and the following was written before I saw that reply to you.
Hi Confusedadult,
I completely understand your stress and anxiety! My BPDm and father are arriving next week and have so far "left it open" as to how long they will stay with us! The occasion is my son's high school graduation, and he doesn't really want them to attend.
I would like to offer whatever help I can to you, so here's what I have for now:
1) Remember that you are stronger than you think and that your time commitment so far is for one "meet up" only; if the exact amount of time is fixed, then that's all you have to handle; if the amount of time is open, then perhaps you can prepare a reason to end at a certain time if that will help you.
2) It sounds like you are still have some hurt from things in the past or they might be triggers for you (to avoid).
3) I completely understand your need to preserve progress. When my BPDm wants to go into the past, I usually do not try to stop it before it starts because that is likely to create an immediate crisis. But if I let her start, get to a first point where she pauses (such as asking me something), I use my repeated boundary of the past being absolutely unchangeable. I found that SET seems to work, so something like Support: "I want to help you with the things you want to talk about, and I don't want to push you away." Empathy: "And I understand you may feel hurt about some things and don't want to be hurt again." Truth: "The fact is that no one can change the past--not you, not me. I cannot go back in time and change what was done, and neither can you."
This is intended to stop the return to the past. If you feel up to it, you can prepare to engage in the here and now with her: "But we can look at what we can do here and now, and into the future."
And an additional note here is that my BPDm "feels" her emotions about the past as real and "factual" each time she wants to bring them up. So I have learned not to engage in whether the past is real or correct, but rather focus on the undeniable reality that the past cannot be changed. Sometimes, this requires my "apology" for the past, which might be the general "if I have done something that hurt you in the past, I am sorry... . " but then I go back to emphasizing that no one can change the past. I think the apology is certainly optional for different situations and different people.
4) My experience includes acceptance that when my BPDm builds up a head of steam about what she's going to "talk about" she will likely be driving toward a demand for others to change and give in to her. She also might have to release at least some of that as kind of a "venting." That is why I don't try to stop it before it starts.
5) I completely understand your preference for a drama free day, and I hope you succeed. To prevent drama, your time with her probably will not be about what you have to say (in terms of your feelings and cares). Instead, it might be your going through motions that manage the interactions to a drama free outcome. Unfortunately, successfully being drama free probably won't be "free of work" for you.
I truly hope some of the above might be helpful to you. Please don't feel that you are alone or powerless. Each of us is stronger than we know.

A