My youngest sister recently passed away and my other sister is complaining that I'm not helping with the preparations for the funeral. And the reason is because I haven't fully accepted that she's really gone. How can I help prepare for her funeral? It feels like she was JUST alive only yesterday. I just haven't accepted it at all.

On the other hand, be prepared for her to say that SHE needs YOUR support. Because she may be feeling the same way as you, and ALSO like she's stuck making arrangements. The best compromise might be to do things together and get through it together.
God bless your family!
Once again, I'm terribly sorry for your loss, I know what its like to lose a sibling. Believe me, time will never heal what happened, but it will make it much easier to deal with and accept.
My family tried to insist that I see my dad lying in his coffin but I've seen so many dead family members in their coffins that I know it destroys my memories of them, so I refused. Instead of being able to picture them in their favourite chair or place, I can never get past the image in the coffin.
We can only do so much at a time like this, so don't push yourself too hard. Ask your sister to understand that you can't cope.
I'm so sorry for your sad loss :o(