Im very sorry for your loss. It was very hard on my daughters when we lost my son. My older NT daughter called me every day, she wanted to stay on skype with me for about two weeks after all day long. Its harder on my Aspies and its really hard on me. My younger son is only 9 and he typically does not want to talk about it, same with my daughter who will be 20 next month. Im told I am handling it normally, I cry all the time and I used to be very "unemotional"...I felt emotion but expressing it was different until now.
I have two brothers so I dont know what its like to have a sister but I can imagine its very difficult and maybe the same. I think the best thing to do is just to let things happen naturally, cry when you want to. I have to be a bit careful because it upsets my 7 year old autie and she doesnt understand.
Death is really hard to explain to kids in general and kids with autism it can sometimes be even more difficult.
Again, Im so sorry for you!