She only vomits when she's in her crate?How often is she in there, and for how long each time?Does she always do it, or only once in a while?How does she react to being in the crate (meaning..does she go in willingly, or do you have to place her in there)?
Thanks for answering!
Sounds to me as if your little girl might be having a little kennel anxiety. The reasons could be everything from her having a bad day to a noise outside that upsets her.
Since she doesn't do it often, there are a couple of products available that work really well on anxiety dogs, and don't require you to have her use them all the time (so you could only use them when she's in the kennel):
A couple things you could try would be:
Melantonin is an over-the-counter drug that can be used to treat some anxiety issues in dogs. The dose you would give would be up to 3 mg given orally whenever necessary up to every 8 hours. More information can be found here: http://www.petplace.com/drug-library/melatonin-melatonex/page1.aspx , which includes risks, warning signs to watch out for and other bits of useful information.
Try a DAP collar. These are collars that are impregnated with a man-made version of the dog appeasing pheromone, which is a pheromone that nursing bitches give off to their pups to help them feel calm and secure. It's something that humans can't smell, but it has an amazing effect on dogs with anxiety and other issues. Although you can find them at your vet's office..you can also find them online at places like Amazon.com and Ebay for much cheaper. Just make sure they're DAP brand, as they seem to work better than some other versions.