As to your original question seeing as we all got side tracked by the gorgeous puppy - there is no reason at all why spaying your pup need make her fat. It is not the operation which makes them fat it is usually cause pups are done at 6 - 8 months and then people go on feeding them like puppies when they have finished the realy frantic growth spurt. Keep an eye on her weight and adjust your food amounts to suit and you won't have a fat dog.
There is no reason to be concerned about the operation. Most semi experienced vets would have done so many of these they can do them with their eyes shut - very routine surgery.
Now all surgery carries some risk but personally I wouldn't keep an entire bitch for any reason in the world. In fact I will be getting a male afghan cause they need to stay entire until their adult coats come in apparently, otherwise you end up with a thin dodgy coat and there is no way I'm going through two or three heats with a bitch couldn't think of anything worse!