Hi dotterof1
Welcome back here
I typically do the best I can to not let her bother me. However, when she does, how can I prevent myself from full-on irritation?
I have an (u)BPD mother as well and one thing that really helps me is to drastically lower my expectations of her. Instead of fearing that she might misbehave I expect her to misbehave and prepare myself based on what I've learned form past experiences. This helps me to be less shocked when she says or does something inappropriate and also enables me to respond better to her and set and defend boundaries when needed.
Part of me feels like thinking, "you know [xyz] will likely happen, expect it and laugh in your head when it does." That's usually what I try to do, but this time there will be in laws around that don't know her and may be shocked at certain things... .I'm not fully prepared mentally on how to deal with it.
The in-laws don't know your mother but are they aware of the fact that she has BPD?