I just woke up yo izzy crying in her pen, which is not like her...Took her outside and she had diarrhea

I got some samples of Wellness small breed dog food ( because she was getting bored with natural balnce, VERY VERY picky ) and i mixed some in with her natural balance..She picked out ALL the Wellness and eat that ONLY.

when she was done she looked at me like I was witholding a treat so I gave her alittle more (yes i know, very stupid!)
So could eating the Wellness give her diarrhea?