There are several different interpretations of the history you gave. I am not clear on how long ago you changed the food. Certainly her not eating the Royal Canin could have been a sign of some other digestive disturbance not related to the food. Also many puppies will start reducing their food intake around six months as their growth is slowing markedlhy. I have to assume she feels good otherwise since you did not comment on her attitude.
The vomiting is what is the most concern as that could be a sign of digestive upset not related to the food at all. You can give pepto bismol or kao pectate at about 1ml per 5 ;bs body weigh orally 3 times a day. See what happens. If that seems to calm things down go back to her original food and stop the protectant. If all is well is could have been the food change. I know this advice may seem a llttle sketchy but it there are a lot of variables, please keep me informed.