I give you kudos for be concerned, but is you concern going to be helpful to your sister or will it hinder her? When someone is sick they ususally revert, so this might be a time for unconditional positive reguard. My first suggestion would be to use more empowering words then "yelled all kinds of insults half truths and just plain delusioal BS." That is not going to help her. Perhaps this might help "Dear sister, I love you. How can I help you?" might be alot better.
Chronic illness/pain can make life very difficult and therefore affect personality. (any mental health issues are considered secondary in a case with chronic illness) In all honesty a high fever can cause delusions, which fever is common with crohns that is out of control. Meds can also do this (remember roid rage?).
You have not given us alot of details on the state of her life and your relationship with her. Since I see that you are not in the same state I wonder how close you are? I am not saying it is impossible to be close when you live away, but it does make things more difficult. How close are your sisters to each other?
Well I want to give you a perspective of what your sister is going thru: how would you feel if you had the stomach flu all the time for years? If you had less bowel control than a one year old? And in so much pain it feels like you are being tortured? It would not make you exactly the easiest person to be around. Especially if you have crummie docs and you need someone to advocate for you.
Believe me if your family is not around for you and helping you, you might get mighty peeved. Crohns can be alot like doing chemo if it is not well control. Now not all cases or times with crohns is like this, but I am trying to help give you a perspective here.
If your sister had cancer how would you help her?
Hopefully you would be there to help her go to doctors appointments, chemo, and just generally help her out because she would hardly have to energy to take care of herself (i.e. make food, do dishes, laundry etc.). Or else you would arrange help for her.
I don't mean to be harsh, but I do want you to understand where your sister is at possible at right now.