The concern that everyone has about taking there dogs to the SPCA or another low cost clinic is that your dog won't get the same personalized treatment she might at your vet....that at such a place she's just another number and not an individual.
I've stepped in on many of these procedures at such places and the way I look at it is that's usually NOT true, and a positive way of thinking of it is that those facilities are much more used to dealing w/ spays and neuters of critters even smaller than your little McKenna. Puppies and Kittens that weigh far less than she does.
So they're used (more experienced) w/ dosing smaller animals to do this operation than your vet most likely is!
jm2c.