Hi, Is she wormed every 3 months ?
As one of the major and most common symptoms of worms is throwing up and then losing nutrition, therefore losing weight.
Has she been wormed? Internal parasites can prevent a dog from losing weight and they can also cause them to vomit. If she had fleas at any point in her life she could also have a tapeworm. Most wormers only handle the run-of-the-mill internal parasites like roundworm, hookworms, whipworms, etc., and a separate wormer is needed to kill the tapeworm, but there IS a wormer that you can get from your vet called Drontal that will kill all internal parasites INCLUDING the tapeworm.
How long after eating does she vomit? WHAT does she vomit? Does she vomit food or does she vomit a foamy, clear liquid? Some dogs overproduce bile and stomach acid and when too much time elapses between meals or a meal and a snack they will throw up a clear yellowish foamy liquid. This is quite common and it's easily dealt with by feeding your dog a couple of smaller meals a day rather than one large one, and then a couple of cookies as late at night as you can manage them, preferably after midnight.
If your dog is vomiting food or anything of substance, then you need to make an appointment with your vet to determine the cause and do whatever necessary to stop it. Please keep us up to date on how your dog is doing.
Ghilly
Pepto Bismol can be used for dogs (but is toxic for cats!)
There is some helpful information on this site regarding side effects to expect, and contra-indications:
http://www.peteducation.com/article.cfm?c=0+1303+1459&aid=1456
Pepto Bismol comes in different strengths so it is important to choose the right one. Normally, regular strength Pepto Bismol is the safest type to use. The dosage of the medication will be determined by the size of your dog.
Generally, the advised dosage is 0.5-1ml of Pepto Bismol per pound of weight. It should be administered every 6-8 hours. If you're using the tablets, that is equal to ¼ tablet per 20 pounds of weight every 6-8 hours.
It would be wise to check this with your vet, if it's possible to call them?
Really by far the best thing to do, I think, is to just fast your dog for 24 hours, allowing ONLY water, then start with plain boiled rice, followed by plain boiled chicken added to the rice, gradually introducing her regular food.
BUT what you said about her being really skinny -and now she has stated throwing up -makes me think she could have some underlying problem here, which needs to be checked out with the vet. So it might be a wise thing to make an appointment with her vet for early next week, even if her stomach settles. SOMETHING is causing her to either lose weight or not be able to gain any.
I don't know quite how you are going to do this, but please do anything to stop her getting to scraps the neighbours are throwing out. Some of that stuff could be very dangerous for dogs. Dogs cannot eat everything humans can.