Don't feed 3 different things - that will upset her stomach for sure. Throw away the Pedigree. Wellness is fine, but if I remember right the kibble is huge so maybe smash it up a little? Don't just feed chicken and rice, it does not have enough nutrients. If you want to start cooking at home you need to look at supplements and variety and all sorts of stuff. That will take more research than you can do in a few days. Once in a while for a tummy ache is fine, but they can't eat chicken and rice every day.
My best ADVICE is to go buy some Merrick canned. It's really wet, Wingaling is my favorite, and you can even mix that with a high quality kibble. There's no way your dog will turn it down and it's just like feeding chicken (it's WHOLE chicken wings) but it has all the nutrients your dog needs.
www.merrickpetcare.com
Good luck!