Confidence, and power. Several years after her second breath, Kate now knows fairly well just how strong she is. The downside, of course, is that she also knows how much the nature of that power has affected her, and so she's largely dropped out of competitive battling as a result, out of the fear that she'd go too far and end up permanently injuring another trainer or their pokemon.
This is how she looks when she meets her eventual-husband for the second time, as in a curious bit of time travel, she ends up back in the exact same time and place as she did the very first time, when she was a kid.
This also features Mustang fully evolved, and the other main member of her Alola crew, "Kommo-dore" Perry. The latter is her primary sparring partner at this point, as she's well past getting anything meaningful from practicing against mortal humans, and while Lee is arguably stronger than him, Perry is much tougher.

Art by Kimmy_arts