What should I do about this friend...?

So my best friend, lets call her Jess, well I love her and all but she does a lot just for attention. Anyway, we were at school and she said when we go to the dance after school she was going to pretend to cry and see how many of her friends cared. I said, "I want to enjoy the last dance of the year. Do I have to comfort you for fake crying because you know I'll always be there for you?" she agreed that I wouldn't have to comfort her because she understood that I found it a little ridiculous that she does this kind of thing. Well at the dance one of mine and Jess's best friends, lets call her Sydney, comforted Jess. Well my other friend Natalie was actually upset because her boyfriend had broken up with her at the dance, so I was comforting Natalie and not Jess. Now today Sydney sent me a very nasty text accusing me of being "a ***** and not caring about my bff's feelings because I'm too y." Well I simply replied with, "I do care, I love her to death, but you don't understand the full story." This caused Sydney to continue calling me nasty things and accuse me of having too big an ego to admit my mistake. Well eventually Jess admitted to Sydney that I was not lying and that she really was just trying to get attention at the dance. Sydney still refuses to talk to me and is still very angry at me for this same reason. This isn't the first time she's done this and I know I'm not a ***** to my friends on a daily basis because they all admit to me (and each other) that I am one of the nicest people they've ever met and that Sydney is out of line with this. I'm wondering if its even worth being her friend anymore, what would you do? I've tried to listen to her side of the story but it doesn't make any sense.