Britney is turned three in May and I STILL haven't gotten her spayed.

I've scheduled appointments to have it done and then cancel them because I am SO AFRAID. I don't know what I would do if I would lose her. She's been through so much stuff with me (nothing bad.. just like move from VA to Philadelphia and such), so she's like a child to me! It worries me sick just thinking about it.
I REALLY need to do it soon though. I am thinking that if I schedule a last minute(ish) appointment than I can get it done without canceling. I will most likely be using the same vet that neutered Brooklyn as we were pleased.
What kind of questions should I ask when I call tomorrow morning? Should I get blood work done? How far in advance should the blood work be done prior to spaying? I know this might sound really dumb- but is there I better day of the week than others to have the surgery done? Anything else?
Thanks guys.