I really think you answered your own question.
It is obviously the Pedigree. There is something in there that doesn't agree with her. Why don't you stop that and see how she does? In my opinion, Pedigree is a very bad food to feed. If you want to give moist or canned food have you tried Evangers, Evo, Innova, Canidae, Merrick... They are way higher quality. You can go here:
dogfoodanalysis.com and look for 4 or 5 star foods. Six star are the best but it all depends on how much protein you think a Yorkie should have. The six star usually have the most and these foods can be too rich for Yorkies.