Kate the Hedgehog is actually Kate transformed into a pink Mobian Hedgehog that resembles Amy Rose. She feels awkward around this and she helps Kristijan with the quest to get back to normal. She also gets back to normal at the end and she's also featured in the two new series.
Kate the Hedgehog as she looks like in the serie Mysterious Mobian Secrets
Kate the Hedgehog as she looks in the serie The Good, The Bad and The Mobian