Sister getting married, what do I do?

Ok lets lay some ground thingies first

1.Me and my sister barely ever spent time together but when we did we usually had fun
2. My sister is really good at getting people mad at her
3. shes only my half sister (not getting into that my family is pretty confusing) and lived with her dad half her life untill he sadly died (we miss him so much and it was not to long ago (less then a year)) and then she moved in with us for a while but then got my mom pissed off so got kicked out and then moved in with her boyfriend(fiance now) (and 2 other friends)

Ok heres the deal, this Christmas my whole moms side of the family found out that she was engaged, but...I dont know what to do about it... I want to feel happy for her, I really do but...well...its really hard to when shes been so mean my whole life...me and my cousin Jessie were talking (the cousin that talked to some peoples in chat on XMas) and well...when her dad died Jessie and her family all went to the wake and funeral even tho the wake was on my jessie's brothers birthday...but my sister never even talked to them much and stuff...it seems my sister is soo unappritiative (sp?) and immature and we dont no to be glad for her or not...shes only known this guy for a few months (maybe 6) and well...hes a really nice guy we all like him...but i think she cant handle it...I dont think she is mature enough...soo do I go against what I believe and pretend to be all really happy for her even tho she was never there for my accomplishments and congradulated me and spent time with me like a normal sister would...or do I just not talk about it and well...not talk to her like I usually do?

Its hard when you face this kinda things cause...Part of me really hates her for not ever being there for me...

(btw I REALLY like her fiance 1. hes hot! 2. he is really caring and took her to the hospital when she was sick)

Gosh seems an awful lot going on there,

I would suggest that you do what you feel is right for you, Not your family, She is your sister and your connection with her is between you and her,

If you have something to say to her give her a call ask to spend some time with her, See if you can both have a girly chat about the things that are bothering you...

She may not be ready to get married but that is her choice, support her and be there for her if things go wrong, thetas about all you can do as a sister, love her... love her despite any problems that may surround you both,

I would say, to have a "man to man" conversation with her. just go and tell her how you feel, and say its her descion and you'll be cool with it either way, but you just think its best that she wait a little longer before she marries this guy, and to me it honestly sounds like its gonna end, or she may need a little longer than 6 months of just knowing the guy, let alone dating him before marriage.
just tell her exactly why its not a good idea, and in the end she'll choose, but at least she was shown the other side, and I agree with ya, it doesnt seem right time for marriage with her and the situation and all. good luck, just tell her how you feel

I'm sure the parents have already done a thorough job of warning her about rushing into marriage. Voicing your concerns are just going to add to the existing tension. Remember this rule...treat others as you would want to be treated. Put yourself in her shoes...what do you think SHE would want you to do? What do you think you'd want her to do if the roles were reversed? Then perhaps you'll have your decision...