Dehydrated kitty

We just brought my kitty back from the vet from being spayed and they told my husband she was dehydrated. I don't understand.

I give her water all day, everyday.

We feed her wet canned food 3 times a day. I even put a little water in it to give her more fluid.

We do not leave dry out. I only give her dry food on top of her wet food to entice her to eat and to satisfy her dry food addiction.

Could she be a dehydrated because of not eating or drinking fom the night before. We were to stop it by 7 the night before.

Any advice?

does she eat all of the wet food? if she eats enough wet food for her growth and development, she will get enough moisture, barring some other medical condition. it must have been from the 'nothing by mouth' before surgery. 

Perform the turgor test for skin elasticity: Gently grasp the skin at the base of your cat's neck and pull it up. If it springs back quickly, he is hydrated; if it is slow to retract, your cat is dehydrated.

Press your finger against your cat's gums. When you remove your finger, you will see a white spot where your finger was. In healthy cats, the pink will return in 1 to 2 seconds; any longer and your cat may be dehydrated.

A lack of sufficient hydration will cause your cat's eyes to appear dull and sunken.

Dehydration will cause your cat's gums to feel dry and sticky, rather than slick and moist, and his saliva will have a thick consistency.

It will be the fasting that has made her dehydrated and she will probably get over it very quickly now she's back home.

Thank you.