Yes, get the lab work done to determine she can handle the anesthesia. It's worth the peace of mind you get. Had it done for Jerry when he had his dental.
Tabitha was about 3 lbs when she was spayed. Biggest concern was keeping her from being too active the week after surgery. She bounced back really easily. Jerry gets sick to his stomach after anesthesia, so I know not to feed him that evening while it's wearing off. It's funny they take it so differently (they are littermates).
Try to relax. You can search the threads on here and nearly everyone posts when it's time for their pup to be spayed or neutered--then, they post when it's over and they feel relieved
A little nervousness is normal. Anxiety that keeps you up at night is not. She will be fine. So will you. Take Care.