Very sorry for your loss. I would send you the chicks you so wish for if I could.
There will be "other" dances and "other" boyfriends and "other" chickens and "other" shows, but there will never be "this" dance or "these" chicks or "this" moment again. I am sorry you are going to miss out on so many things I know you wanted in this final year at home and in 4-H.
I will ask that you not retaliate against your sibling. It is your parents job to be parents, even when they will not do it.
Try not to hate her too long. Carrying this baggage through-out life will get very heavy. I hope this was a case where she simply didn't believe you when you said they would die, that she did not try to kill them.
It was not an accident, she deliberately did something against instructions. She should bury the chicks, as previously suggested. My 11 yo had to watch our efforts to revive a chick he had played a little too rough with. We failed, it died in front of him, in obvious pain. This was very emotionally educational, I think the fist time I've seen remorse in this special needs kid. I think burying the chicks without any kind of funeral fruppery would also be educational.
When she complained about the light hurting her eyes, that should have been a clue to remove the brooder from her room. It was, after all, making her uncomfortable, and the family was callous to her needs by not removing it. Hey, if we are going to be judgemental, we'd better call that one. These were not her banty chicks, correct? They should have been somewhere else if they were bothering her.
As a Mom of an Elder Son and a Younger Son, I can tell you it is often difficult to determine the greatest amount of fault in these situations.
At our house the Elder tends to be bossy, and expects the younger child to obey to the letter and without question as if the elder were a parent. The younger doesn't see the validity of this (would you if the roles were reversed?) It is hard for the parent to see the Elder behavior as anything but bullying when done so repeatedly. It isn't a matter of thinking the youngest is perfect, but of protecting them from what appears to be a physically bigger and threatening (and often enraged to the point of unpredictability) elder sibling. I'd be on my eldest's side more often if I didn't think he were about to injure the younger.
In your specific situation, your parents have to love your sister more than the birds. They will have to deal with the fact that she put the family and its property in danger and that she killed much cherished and expensive family animals, who suffered as they died, and that she acted even after being told what would happen if she did. That will be easier for them to do if they are not fearing for her well-being in the face of your (completely understandable) anger. Take a walk. Cool off. Give them space to deal with it.
It is soooo hard being a parent and be expected to make every call right. Cut your folks as much slack as you can. If they are home-schooling you, I am willing to bet they are already making huge efforts on your behalf.
If you cannot see this, then concentrate on keeping your test scores up and getting out of there.
Make peace with your sister when you can. You'll be her sister forever (gulp!) so try to get past this eventually. Grieve, Breathe in, Breathe out, Move on.
Gee, I wish I could come up with this stuff when dealing with my own kids.....