One of the Kingdom Hearts franchise's lasting charms is the interaction between its original characters and Disney characters. Sora, Donald, and Goofy have been the main player trio for many years, and they're just as significant to Sora as Riku or Kairi. Riku himself also has a close bond with King Mickey, showcased especially in Chain of Memories.
However, Kairi has yet to get her own Disney companions in any of the Kingdom Hearts games. She had Merlin as a mentor, and has some connection to other Princesses of Heart, but she hasn't formed a friendship with any of the Disney characters like Donald or Goofy. That could change in future games, and there are already some good picks for Kairi's potential companions.
Minnie and Daisy
Minnie and Daisy would be the easiest answer for Kairi's Disney companions. They're established characters in the games and are directly connected to Mickey, Donald, and Goofy. Minnie has been shown, albeit briefly, to be a very capable white mage. They're both Disney Castle royalty, and have had small parts in the plot of the series so far.
Minnie and Daisy are both relatively minor characters, so it would be interesting to see them and Kairi take on more active roles together. Daisy in particular hasn't done much at all; all that's known about her is that she's in a relationship with Donald and friends with Minnie. It's unclear what her actual royal status is, or what her abilities are.
Since they're both relatively blank slates, there's plenty to build upon if they were to accompany Kairi. They've been left behind by their male counterparts too, so they have that in common with Kairi. It would also be fun to see the two of them in new combat outfits as opposed to their royal dresses.
Lena and Webby
There haven't been any television shows used for the Disney worlds in Kingdom Hearts games as of yet. The 2017 version of Ducktales was a popular cartoon, with a surprising amount of depth and lore, so there's a well of content and new characters who could be introduced to the games. Lena and Webby are two characters with an established bond and have their own combat abilties; Webby is an adventurer and the "fists" of her team, meanwhile Lena is a magical being. They slot in perfectly to the fighter and mage roles held by Goofy and Donald as part of the main player trio.
Since Lena was originally made from shadows, the games' plot could play with the concept of darkness and how it can exist in good people. Webby is directly related to Scrooge and Donald, so her story could be adapted to fit into the Kingdom Hearts universe.
Kairi would actually be the oldest member of this trio, which creates a new dynamic. She has already spent plenty of time with mentors, first with Merlin and now with Aqua. With these new companions, Kairi could be the one guiding others, or find common ground with them. That dynamic would be a great opportunity for her to show more character development and grow meaningful relationships outside of the Destiny Islands trio.
As of now, it's unclear if Kairi will ever get her own adventuring party. Historically, Kairi has been sidelined in the games and hasn't had much of chance to shine. Since Melody of Memory and Re:Mind gave her some screentime and set Kairi up to train with Aqua, it's possible she may become playable down the line. However, the Kingdom Hearts franchise's pattern thus far makes it appear unlikely.