I agree, she is likely a White Rock. White Rocks have red earlobes and yellow legs, just like her. True Rhode Island Whites have rose combs, or at least that is the only type that the American Poultry Association recognizes. There are some single combed Rhode Island Whites, but they aren't really RIW, as they aren't in the APA Standard. RIWs are rather rare, and White Rocks are common, so that is how I conclude that your bird is a Plymouth Rock. Pretty girl!