When Cooper wants Mike to create another Dougie (presumably for Janey-E and Sonny Jim), he entrusts this task to Mike, who says, "I understand". Cooper cannot make a Tulpa himself -- he has to ask Mike to do it for him.

Similarly, maybe Mr C. didn't know how to make a Tulpa at first, either. Every move he has made in the last 25 years has been calculated and precise -- he knew he would eventually need to make a Dougie Tulpa, in case Cooper tried to take his place in our world. So, he takes Diane to the convenience store where these otherworldly beings exist -- possibly so they can assist him in creating a Tulpa, or show him how to do it? Or, more likely, maybe he had to go to the convenience store to get one of those seeds. He obviously can't go to the Lodge and get one from Mike.

The point I'm trying to make is, he doesn't create Dougie until years after he comes into our world. I just assumed he made Diane first for practice. I don't think Naido has anything to do with Diane whatsoever.