The yellow fluid is bile indicating her stomach is probably empty when she is being sick.
If she is fed only once a day you might try splitting her meal in half and feeding twice a day and see if that solves the problem.
Sometimes dogs that have swallowed bone chips or other irritating items will be nauseous when their stomach is empty due to the irritation of the hard or sharp items or something that is too big to pass through or vomit back up like a soft toy. If you are missing any toys or something from around the house that might be the problem.
Dogs sometimes will vomit when they have parasites such as worms that also can irritate the stomach.
This could also indicate a more serious problem such as liver disease.
Dogs can even have a reflux problem similar to the ones some people get. For this some of the over the counter drugs may help.
Whatever the problem is your vet may be best able to figure it out and prescribe the right treatment.
You might want to bring in a sample of the vomit and have the vet check that. A stool sample check may also be something your vet will want to do. An x-ray might show a foreign object or a tumor, and bloodwork might give you an idea if the problem is with the liver.
Sometimes the problem can be a food intolerance to something in her dog food even if she has eaten the food her whole life!
I suggest a vet visit and a conversation with your vet about causes and solutions.
Hope this helps!

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