I am so sorry. You attempted what is one of the most difficult rehabs out there - a baby mouse. It seems absurd that something that is so common and frequent that people kill them wholesale without a second thought is so delicate but it is true. I have succeeded ONE TIME and have tried many (my little Nate lived to be 5).
Every little mousie at the pet shop that gets purchased is one that doesn't get eaten by someone's snake. They are also diurnal - daytime creatures, instead of nocturnal like the little wild ones.
I am so sorry. Rest in peace, Daniel.