Is it okay to let one dog dominate the other?

I had to dogs a cairn and a rat terrier/yorkie/poodle mix. My Cairn Terrier Roxy is dog friendly but she always marks over Reesy and when they play Reesy would pin Roxy down and growl if Roxy tried to get up or move. Roxy is a little food aggressive and when Reesy eats out of her bowl Roxy lunges at Reesy and tries to attack her. My mom says that we should just let them work the whole dominate submissive thing out and in the past this is true. Is this okay?I watched the dog whisperer and Cesar said to not allow dominance period.