
Hi Sheli,
Rescue Remedy is usually effective enough as a short term relaxant. I prefer to use the drops on the nose leather rather than in the mouth. However if you can get hold of the spray version it is safer and more convenient because the one with the pipette is made of glass ;) If using the spray, I'd give her three sprays orally a couple of hours before going and the same again around 15-20 minutes before you leave. If using the drops then one or two drops every half hour for around 2 hours should be sufficient.
There are other homeopathic treatments & herbal alternatives but with herbal meds it's best to check with your vet that what you are using will not adversely react with prescribed medication.
If your girl is only going for an introductory appointment or something which is not likely to result in medication, you could try starting her off today/tomorrow on Serene-UM (available from Pets At Home) - this comes in tablet form to be popped down the throat or in a liquid version which can be added to her food. Using it around 3 days before and on the day of a potentially stressful situation definitely takes the edge off them :) Quantities needed are clearly printed on the box / bottle.
As a footnote, personally I would prefer to work on gently and over time relaxing your dog to the vet situation rather than depending on meds (especially prescription ones) to do the work. Can you try and set up some regular occasions when she can visit, just sit in the reception area for a few minutes, and leave? Then work up to her being petted by the nurse / receptionist / vet before leaving and, hopefully progress to her paying a short visit to a consulting room - similarly petted or treated (if she will accept titbits) then leaving on a high :)
In the long run it pays dividends to get our dogs to at least accept vet visits - some will thoroughly enjoy their time there and others, even if not having had a painful or invasive treatment, just never "like" being there but can be brought around to cope without stressing out completely :)
Good luck, HTH,
Teri