It can be difficult depending on the ages of the younger children and its possible too that one of them will tell her what you have said.
I think I would just say that she has a brain disorder that makes it very difficult for her to control her feelings when she is angry or upset and also makes it difficult to plan ahead. That you know her behaviour is sometimes not okay and you need to give her extra help with this compared to the average person.
It does get complicated later on when siblings are prepared to accept a lot less than parents, especially if they feel that BPD sibling is taking all the parent's energy and attention. (Believe me I know this!).
Boy that is great advice in a short amount of space. Thank you for writing that.
I have been struggling with similar issues... .like just the other night when my 16yo daughter woke everyone up at 1:30 in the morning screaming at me because I insisted she not have her iPhone in her room late at night, but she instead flipped the whole conversation over to why I'm not a good mom (which is bulls**t -- I'm a very good mom, but anyway... .) It ended with her sobbing pitifully and saying she just doesn't know what's wrong with her and why she can't be like everyone else.
The next morning, my 14yo son asked, "What was THAT about?" I used to sugar-coat things, but I don't anymore. I just tell him what the fight was about, and I have told him that she struggles with emotional control etc... He's an understanding kid, but I feel bad that he has to live with this.