I know exactly what you are going through.
I'm going through the same thing right now, actually, though it's not my sister.
(Our youth group's van flipped Friday on a trip to a winter retreat, two of our youth leaders died, and the rest were hospitalized. We've still got one student in the hospital in critical condition.)
I will definitely keep her in my prayers.
I know how you must be feeling, because I've been feeling it, too.
In times like this you've just got to be strong and lean on the Lord.
Trust me when I say I know it will be hard, but putting your faith in the Lord is the only thing that can give you peace and get you through a time like this.
All things work together for good, and God will bring something good out of this, even if you cannot see it right now.
I will keep your sister and your family in my prayers, and will pray for healing for you all. <3
God bless you. <3