It's a large-sized dressing mirror (like one of these) bought from a second-hand shop in Melbourne. It was also smeared with sweat from her stablemate back in Melbourne.

手鏡 ("hand mirror") is likely mistranslated from English "dressing mirror" or "vanity mirror" by a reporter because their equivalents in Japan tend to be smaller.

NNescio said:
important info

they really took the stablemate aspect and made it to be Folkqueen's "Other Personality" quirk. Cafe's defining trait is in danger.