Frequent dietary changes and stress-related occurrences are a good recipe for bowel disease in any pet. If she has been on c/d-s for quite some time already it is unlikely an intolerance to the food, although if there have been changes, there may be some hypersensitivity or allergy to one of the other foods and this may be causing an IBD (inflammatory bowel disease). The first step I would consider is switching her to a food designed for an inflammatory bowel disease eg i/d or a true Vet clinic only hypoallergenic food. Secondly you may need to consider stomach lining protectants. If this does not produce a result, treatment for colitis - specific antibiotics and a different diet - w/d - may need to be considered. Finally if this doesn't work, sometimes a course of cortisone may be considered to tame the bowel inflammation and response however I am not a great proponement of just placing them on this drug without getting a positive diagnosis of an intestinal biopsy.
Martin Slome DVM
Centre Street Animal Hospital
7700 Bathurst Street Units, 40-42
Tel. (905) 771-9855