There is actually 4 ladies.
Lass Persephone: She only goes on the Ferris Wheel in Spring only
Nursery Aide June: She only goes on the Ferris Wheel in Summer only
Clerk ♀ Trisha: She only goes on the Ferris Wheel in Autumn only
Beauty December: She only goes on the Ferris Wheel in Winter only
These are only the people you encounter if your trainer is a male. For female scroll down on this link.