Can cat food cause diarrhea in dogs even if it's the same brand?

Luna eats wellness care for dogs. We recently adopted a kitten, and he eats wellness core for cats. We usually feed Luna first, then let her outside, then feed the kitten. I try to remember to put away the cat food before letting Luna back in, but since the kitten eats several times a day, I don't always remember there is food in the bowl, and sometimes Luna gets to it. The feline formula is much smaller than the canine formula, and there is never much in the bowl. We've had the kitten for about a month now. But yesterday and today, Luna has had diarrhea. I am not sure what else she could have gotten into that would cause an upset stomach. Other than the heat wave, she hasn't been outside more than 10 minutes in the last two weeks, always supervised and then she comes in. And because she is so much bigger than the kitten, I always supervise their playtime. No other changes... she can't get to the little box, which is pine pellets. No different food or treats, no destroyed toys.


Do you think the heat could still bother her even if she's been inside during the heat wave? I haven't taken her to the park, on walks, nothing, it has just been too hot...the only exception has been in the last few days, I have let her out in the backyard in the mornings while it was still cool enough. She always has access to water, though, and this just started yesterday. I think I'm going to have to put up the gate to the playroom and keep the cat food in there so that Luna just has no access.