Am I over reacting or do I have the right to be upset about the way my sister treats my family?

I am 18 and my sister is 16. She was diagnosed with bipolar disorder but I don't think it is the only reason she is the way she is. My sister doesn't realize how good she has it my parents support her, drive her around to her guitar lessons, voice lessons, and band practice, she has a horse, and they treat her with respect. My sister still fights with my parents over the stupidest things. The reason I believe it has way more to do with bipolar disorder is because she has always had an attitude and it just seems like part of her personality. Occasionaly she is nice but it seems that most of the time she is in a pissy mood. She wrote down in a jounel that she thinks my parents might be abusing her, that really pissed me off because my parents are in no way shape or form abusive! She wrote that my mom attacked her because she threw a lamp and that everyone in the family makes her feel stupid and puts her down. The only time my mom ever physicaly did something to her was after my sister threw a lamp at her so my mom slapped her (not hard). I have gotten coffee dumped on me for rolling my eyes at her and my mom fighting, she will throw stuff at me if she gets mad enough, she even hit my boyfriend with a remote and left a huge welt on his arm because she was annoyed by him. Tonight I asked my sister if she would go upstairs to watch tv so i could watch a movie. ( I asked her because usually she sleeps in the room upstairs instead of her own and I didn't want to be up there in the middle of a movie if she wanted to go to bed) She then started yelling at me about how she doesn't sleep in there anymore and she sleeps in her own room and I wasnt fighting her about it and she kept yelling and I was asking her why she was being so rude to me and what I did and she was yelling about how im not nice to her (I actually try not to talk to her and avoid her most of the time and if I do say anything that upsets her its just me calling her out on her behavior) as I walked upstairs my sister called me a *****, my mom heard but didnt do anything, I was pretty upset and she came in to talk to me and told me I was over reacting and all siblings are like this. When ever my sister does something that upsets me like throw things at me call me names and even hit my boyfriend my mom is always mad at me for being upset with her. I feel like i get punished for my sisters behavior. Am I over reacting?