The lesser yuki-onna that they dumped on Frost to handle was a spirit monster focused on magic. Its appearance was that of an ugly young humanlike girl with a malevolent expression. Snow white skin and adorned in tattered robes. Regular yuki-onnas were quite beautiful and rather mild in nature but lesser ones were more bestial and far weaker. The lesser yuki-onna was around upper D-rank in strength whereas a regular yuki-onna would be C-rank at minimum and possess intelligence, far too strong to be birthed by a low level monster lair such as [beginner's ice magic].
In the native kingdom of Glasson where the frost lilies said they hailed from; a large part of the citizens were spirits such as yuki-onnas. They were considered at the level of being able to mingle with sapient races, a far cry from the abilities of their lesser kin.