Kate's long ponytail look is firmly associated with her mid 20s, as she's kinda in the most adventurous phase in her life at that point, fully determined to figure out what's going on with her, both the time travel nonsense that seems to keep happening, but also now her exaltation as well, as she slowly starts to explore what she's now capable of and understand parts of the world in a new way.
This pic also features Shao Mei evolved, as well as another member of Kate's Alola crew, the Ninetales Śnieżka (aka "Snowball", or "Snow White" in Polish). The latter is Gaul's best friend (and probably mate), and has a bad habit of prancing home out of the woods, all dainty and majestic...covered in mud, leaves, and sticks, making Kate (and usually another family member too) spend a couple hours brushing her and cleaning her off XD. She does, however, function as a wonderfully pillow on hot summer days, being naturally cool as an ice-type and having such fluffy tails.

Art by Kimmy_arts