I'm guessing a Production Red.
Production Reds are descended from Rhode Island Reds, and are still quite similar, but the hatcheries selected for better egg laying and didn't care about details like shade of red and color of earlobes. So they often look a little bit "wrong" for a Rhode Island Red (like this hen with some white in her earlobes and some black in the feathers on her side.)
Or she could be some kind of a mix, because it's fairly common for people to hatch eggs from a mix of breeds in a backyard flock. Some of the mixes can look almost the same as the parent breeds, while some others look very different.