the vet that spayed bonnie also told me she wouldn't need any pain meds, and I ended up going to a different vet a couple days later to get some because i could tell she was in pain. and we never went back to that vet. just my opinion, but i think you definitely want to take some pain meds home with you after your chi is spayed. Even though she's so little...they can give her liquid meds in a tiny little dropper. the vets have formulas to calculate the dosage based on your dog's weight. Both mine ended up getting 0.1 ml once a day, and for oscar they even gave me droppers with the meds already measured out.
If they want you to leave your dog overnight, make sure that there will be someone there all night to monitor her. and if you're really not comfortable leaving her, insist on taking her home. if they won't let you, find a vet who will.
I know it's soooooooooooooo hard not to worry about your baby being spayed, but it's really a very routine procedure. We always hear the horror stories, but the vast majority of spays go fine with no problems. my dog bonnie is under 3 pounds and had no complications (other than post-op pain). the most important thing is to find a vet that you are comfortable with. hope this helps, let us know how it goes!