Doggie Diarrhea

I would get her off the Purina but do it very slowly. Introduce a few pieces of the new food and increase the amount every two days and reduce the old food by same amount. Here is a link to a review of all dog food along with the reasons as to why they received the rating. You can see all the five star dry and canned. Over to the right is a list of reviews of all dog food by brand. The site also list any recalls and you can sign up to receive emails of recalls as soon as they come out.
http://www.dogfoodadvisor.com/dog-food-reviews/dry/