Could you possibly get her father involved, after all it is his kids we are talking about. This behavior is very immature for a 17 year old, she should be able to understand that egging him on only makes the situation more difficult. When the situation starts to escalate tell her, I know this must be frustrating to deal with your brother's anger issues, but by bullying him back it only makes it worse, how in the future do you think we can handle this better? By asking her for her input you won't be preaching to her, but offering her a life line.

Welcome to the site!

-CK

I would sit both the mother and father down and talk to them. If however that doesn't work you can always have them take her to a doctors visit with him and have the doctor to explain things. After trying that if it still didn't help since she lives in YOUR house I would stand up to her and start taking things such as the phone, tv, dates and so on. In the long run it will cause her to respect you especially when she has kids. Remind her Karma isn't nice and the way she treats her brother will come back to bite her. Remind her one day she will want kids and she too could have a child whom has special needs. It took us some time to get my 6yr old to understand her 4yr old brother isn't like her and he doesn't understand things we do. She's 6 and understands and if a child can then there's no reason a teen can't. I'd also tell her if she can't respect him then she can move to her mothers or some where else and see how it helps.