Ashley, I'm so sorry to hear about all the drama w/ your sister. Sadly, I can totally empathize. My sister told me how selfish I was that we were having a DW & that no one (read: our brothers) would be able to afford to come. Well, the parents were helping everyone get there so that wasn't an issue. She didn't come to the wedding & never really congratulated us. No call, card, email or even text. I sent out a link with some pics & she later responded that we looked really happy so I guess that was my congrats. I happen to know that she's miserable in her own life so there's a lot to what the girls here are saying.
Just realize it's not about you; it's about her and she's just too self-involved to be able to get over herself. Some people are seriously narcissistic/insecure & just can't really be there for someone else; my sister being one of them. We can't change them, but we can certainly decide how we want to deal (or not deal) with them.
Like LeAnne, I would lay it out for her & let her know how you feel. Then you'll have done what you can and the ball will be in her court, so the speak.
Good luck with this sticky situation! I wish you all the best!