
Id not be surprised if its the fact that pedigree is rubbish food!
Dont change her yet, do some research into foods (the most expensive, the most advertised etc are not necessarily the best!), then change her to what you decide upon, adn stick to it.
Vaccs can upset pups, as can frequent food changes, as can the move from one home to another, as can a large dose of worms.
But pedigree is well known for giving dogs the squits, and whilst it might be more expensive than the food she was previously on, given that a can of pedigree complete meat is a min of just 4% meat -- you gotta wonder what the rest is! (heres a clue, water, sugar, oils, colourants flavourings cereals etc)
Em