I would describe Pearl as a blue mackerel tabby domestic shorthair. "Blue" is the technical term for "gray" in cats. Spots on the belly are normal for mackerel tabby cats. She is a lovely girl! Most cats are not any particular breed.
Pearl does not appear to be silver tabby in color. Silver tabby cats have black stripes on a white background, and the base of each hair is white. Blue tabby cats like Pearl have gray stripes on a beige background.