All available sources agree, this is how it happened.
My sister walks into a bar covered in blood.
My sister walks into an Irish (American) pub covered in blood.
My sister walks into an Irish pub in New England covered in blood.
My sister walks into an Irish American pub in New England, after the Patriots won a football game, covered in blood.
Everybody in the pub (except, presumably, the workers) is drunk out of their minds. They're looking at this woman who just walked into the pub and is covered in blood.
Does my sister explain why she is covered in blood? No. She's my sister. She tells her friends, "Come on! We're going to have the best Christmas ever!"
Because that totally makes sense coming from someone covered in blood without explanation.
I've never had venison before. I'm not overly impressed, but neither am I disappointed. I don't think it made yesterday the best Christmas ever. But it was good meat.
What happened is that my sister got into a car accident. She was fine. The car was mostly fine. The deer was, thankfully, killed instantly.
After my sister found out that last part she was completely fine with the situation and, as noted by her when she was covered in blood, looking forward to the best Christmas ever.
Before she found out she was terrified that she'd find that the deer had been terminally wounded but was still alive and suffering. I can see how scary that would be. The only decent thing to do in that case would be, as she said, to finish it off. But intentionally killing something isn't really something either she or I want to do. (Though she's more comfortable with getting to know things which are going to be killed than I am.)
Also, I think though she did not say this, there would probably be lingering doubt. What if you thought it was terminally wounded when really it would have recovered? Then your attempt at mercy would actually be a bad thing.
Anyway, that didn't happen.
The deer died instantly. However, it landed wound side down. When my sister approached it looked like it was fairly pristine, just stunned. Then she lifted the head. Which is when she got covered in blood.
Before the meal she said a grace in which she thanked God, the deer, the car that killed the deer, and her friend who prepared the deer for eating.
And that, basically, is the kind of person my sister is.