not in milk. Many cats are lactose intolerant, and while she is poorly i wouldnt suggest experimenting to see if she can tolerate it or not.
If you have some evaporated milk, goats milk or specific kitten milk then yes. I would also scramble the egg first to cook it.
I give raw eggs as part of a barf diet (raw diet), however there is always a minute risk of salmonella, and raw eggs do contain proteins which can inhibit vitamin absorbtion. Egg whites inhibit, egg yolks promote so they do balance, but again with a sick cat, best to cook the eggs.
try some other foods to tempt...
goats cheese
pilchards/sardines
tuna
boiled white fish (coley)
boiled chicken
hotdog sausages (yep it can tempt their appetite)
cooked minced lamb
Anything to get her eating now.
Once she is eating you can go back to your normal diet for her. If she hasnt eaten by this evening i would be ringing the vets again and expressing your concerns.
HUGSXXX
and for what its worth you did the RIGHT thing getting her speyed! I foster pregnant cats and kittens for a rescue. I see what happens when things get out of controll, and all the unplanned litters and kittens. Ive seen queens die during birth, kittens die and young girl cats die early because their bodies are just worn out with back to back litters
YOU DID THE RIGHT THING!