Queen Elsa is a Premium Box Tsum. She is a Limited Event Tsum and is not available from purchasing Premium Boxes outside of the event. She was introduced during the Japan event 5th Anniversary Tsum Tsum History (January 2019) and the International event 5th Anniversary Tsum Tsum History (July 2019).
Queen Elsa will freeze surrounding Tsums in a chain. The chain can then be broken with a tap. Her base time is 3.5 seconds and her base radius is SS.
Try to connect as many chains as possible and clear the frozen tsum tsums in a tap as quickly as you can, since you earn more point for how many tsum tsums would be cleared.