Im sick of bridezilla.. should I quit the wedding?

So my sisters wedding is coming up, and she's acting like a spoiled bridezilla brat. First she asked me to dye my hair because my hair is brown and the rest of the bridesmaids hair is blonde. Well I told her no and she guilted me into it, telling me its her one big day and she wanted everything to look perfect. So I agreed. Now she thinks its "too" blonde and that I should go get it fixed. I dont have the money for it and she refuses to foot the bill. Not only that but shes insinuating I need to get my dress altered. It fits me fine but she thinks it makes me look like "a cow" i think her words were and I need to get it let out. What F-ing nerve. Okay so I make the appt to get it altered and this lady is a friend of a friend so Im getting a big discount, but shes not a high known alterations lady so my bride sister decided shes not good enough to do my alterations and I need to use a high cl expensive boutique, yet Im paying for it. LASTLY, yesterday she begged and pleaded I come over and help her with centerpieces, and I did 14 out of 16 and she sat around flipping through bridal magazines and eating pizza. Im sooo done right now. I know Im her sister and maid of honor but I really just want to throw in the towel. Should I??