Why does it all happen at once?

Pocket Mouse died today.
I don't know how or why.
I was driving to school with her in my shirt pocket. On the way there, I felt her move around a bit.
When I got there, I stuck my hand in the pocket to take her out and show Daly (her breathing had improved since yesterday), only to find that... she wasn't moving.
She was still warm.
But not moving.
I don't know what happened.
But I feel really, really bad.
I feel like I can't take care of animals without them dying...
Daly pointed out, "But look at all the other animals you have. They've done fine."
He also said about Pocket Mouse, "Maybe it's for the better. She hasn't really been acting right the past few months.."
That was before my first class.
What does one do with a dead mouse during class?
Well, we went to Daly's car and put her in the jar she had been brought to school in yesterday.
We left her there until our hour break.
We took her into the woods and buried her under a tree, piling nice stones on top of the dirt.
*sigh*
I am sad.
Would she have died if Daly hadn't let me take care of her?