I'm truly sorry to hear that your sister is having to go through this painful episode at such a young age...
There never seems to be any of the right words, let alone the right amount in these situations...
The best is if you can, try to be there, physically, to lend her your kind warmth and presence...
That may be all that she can handle...and above all, she may want to talk...I learned a long time ago that each situation is VERY different...but funerals seem to be the worst and most ackward of them all...
The best in all of this? Just be available... She'll need you...
Again, my thoughts and prayers will be about you and yours...
.
.
.
.