Rose Queen is a local or regional tradition associated with Whitsun processions or June festivals and fêtes similar to May Queen. Annual civic honorific titles are bestowed by local election to particular individuals, typically local young women.
it is likely the Rose Queen tradition developed simply because it was the wrong time of year for a 'May' Queen. However, beyond the name, there is no discernible difference between the two, and sometimes they exist side-by-side. From Wikipedia
