Like Ginger said, hydration is the most important thing you can do until you can get her to a vet. I always worry about parvo when it's a puppy under a year, and sometimes even young adult dogs fall prey to the dreaded virus. Withhold all food until she stops vomiting and make sure she has lots to drink. I would even go so far as to give her Gatorade or Pedialyte because they have electrolytes in them which help to keep the body's electrolytes in balance until the crisis passes. If the electrolytes get too far out of whack (as can happen from dehydration) it can disrupt the heart rhythm and become dangerous, so it is especially important to try to prevent her from become dehydrated. ANY liquid is good, but when their appetite is off, it can be difficult to get them to take anything in, that's why sometimes a flavored drink or even beef or chicken broth (you can make it yourself with a buillon cube) works. If you do give her Gatorade, though, make sure that it's just the plain Gatorade, don't give her anything with anything to zip it up like energy drinks or Gatorade with herbal doodads in it.
Please post back and let us know as soon as you can how things are going with her.
Ghilly
Oh I am so sorry your question yesterday got missed! Did you get her to the vet? And what did they say?
Don't withhold water. If she throws up the water, you definitely have an emergency situation, as a dog, especially a dog her age can dehydrate very fast. Don't worry about her not eating for now. Her system wouldn't be able to cope with food.
I can't tell you what is wrong with her, but it could be many things including Parvo, pancreatitis, havng eaten something which has violently disagreed with her, or something toxic for dogs, or it may be just a bad tummy-bug that has got a bit out of hand.
Whatever it is, you should take her to an emergency vet as soon as you can.
If LITERALLY it is impossible to get her to a vet because of circumstances, then the best thing you can do in the meantime is feed her very small amounts of water very regularly. Small amounts are less likely to be vomited back up. Or Pedialyte if you have any, would be better . Just try to keep her hydrated as best you can.