I would put a bit of honey in her drinking water and get her to drink often until you get her to your new vet. Before you go, pick up your old records with test results it will make the transition much easier.
Can I ask why you have your little one on a lite food? Do you change the food brands often? That sometimes can cause vomiting. At 3.5 years I wouldnt think lite food would be necessary and something could be missing in her diet.
here is a good article
http://www.vin.com/VINDBPub/SearchPB...00/PR00421.htm
hope this helps