Hi Blackdragon. I'm sorry to hear about this agrivating situation. I think we've all been there with people in our lives.
First of all, I would suggest that you tell your cousin that it made you uncomfortable that she just assumed you'd bring her friend home too, and that she should've asked you first.
I would also like to suggest that the both of you have some boundary issues. You need to set some boundries with her as to what is and is not acceptable in how she speaks to you, treats you and that calling you a bi**** is absolutely unacceptable and that you deserve more respect that. By the same token, you don't want to do that to here either.
When someone, like your cousin, is provoking you like that...don't be afraid to speak up. Remind her that you're driving and need to concentrate without being argued with.
As for bp, this sounds to me like it's more circumstantial feelings of agitation, irritation and being hurt by someone calling you such a derogatory name. I would be pretty upset too regardless of bp.
Communication is the key in any relationship and it sounds to me like the two of you need to learn to communicate with one another on a more civil level.
Just one other thing, I believe you said your cousin is pregnant....she is highly hormonal and all kinds of things are taking place for her physically, mentally, emotionally and psychologically. Try to keep that in mind too.
Hope this helps.
TgrsPurr. xo