If it's every once in a while, then it's from hunger. Uni does this as well. She is very picky and sometimes refuses to eat, then voila, foamy yellow barf. If your dog is doing it often, then yes, go to the vet. It could be something else that is causing her loss of appetite.
__________________  The T.U.B. Pack! Toto, Uni, & Bindi
RIP Lord Scrappington Montgomery McLimpybottom aka El Lenguo the Handicapped Ninja 10-12-12 
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