The cat has become the de facto protector of both the dogs, looking after them when they're both sleeping, acting as a buffer between them. It shares the warmth, exchanging the heat and allowing to flow from one place to another. Sandwiched between them both, the cat also serves as the perfect hedge for the dogs, because they can detect slight movements in the cat's body, this can be a sign of things to come.
Although the dogs are in safe sanctuary, they have experienced danger in the past as well. The both work in collusion with each other to protect the cat when a predator approaches, and given how the trio have fierce combative experience, no one dares to encroach upon their territory, even the owner knows better than to cross her pets.