If you do decide to switch foods.. I would do it very gradually... like maybe over a week and a half span.
Most people don't like Royal Canin.. but please also don't put her back on Iams. There are a lot of much much better foods out there.
www.dogfoodanalysis.com has non-biased reviews of foods. Look in the Premium (4-6 star) sections.
And welcome to YT!
