I'd personally wait to switch foods if she has diarreha now. I'd wait until she firms up some first before switching foods.
Is there ANYthing new you gave her in the last 48 hours? Any new treat? More food? Did she eat something on her walk? Anything?
If nothing new was added to her diet, have you tried some pumpkin or yougurt, or partial or full bland diet to see if her tummy settles?
If you want to just try transitioning her to the new food, I would recommend making that transition slow. If her tummy is already upset, you don't want to upset it anymore by switching cold turkey. My girl has a sensitive tummy, and it took me almost 4 weeks to transition her to a new food. Maybe start with 75% of the Eukanub and mix in 25% of the new food. See how she does. If you see she firmed up a little, keep her at the mix for a couple of days before increasing the new food and decreasing the Eukanuba.