There is a product that has been developed that works well to calm cats that are very stressed. It is called Clipnosis, it is a clip that gently scruffs the cat and makes her calm instantly. They are a bit costly right now but work extremely well.
You can also do some Tellington TTouch on her, try some Ear Touches; gently slide your fingers from the base of her ear to the tip, do gentle circles on her ears. Do these touches regularly not just when she needs to go to the Vets.
It Is What It Is