Also recognize the reality of BPD and AVOID any trigger. Learn from this and avoid the trigger next time, which is mentioning anything to do with those people whom she dislikes. Don't mention it. If you go by there again, talk about something completely different and distract her from the fact of going by Bills house.
My BPDgf has so many triggers though and constantly biting my tongue is a hard thing to do. How do you have a normal relationship whilst constantly being on guard regarding what you talk about or what you say all of the time? It doesn't make sense. There are so many triggers that we can very rarely discuss many topics without her garnering some form of offense from the conversation.