I have a Miniture Wieene dog and everytime we feed her she throws it up. There is a lot of mucus in it. It isn't everything she eats because she is not under weight or anything like that..it's just messy and you have a messy to clean. Could she just have a nervous stomach?
This could be a megaesophagus. I recommend a visit tot he vte to be on the safe side. An x-ray is warranted. vetcare