I feel Bonney's story arc is 90% complete, and so far there's nothing going for her to join the crew.
She made friends in the crew, cool. But her focus was always her dad, her dream is to travel the world with her dad. That was her freedom, the objective she pursued Nika for.
Right now, she rescued her dad, and she probably has the key to wake him up from his catatonic state (his memories). Kuma's current condition is already a miracle for Vegapunk. The buccaneer's special trait is still unexplained, and, in Ch 1118, we had Kuma, in his catatonic state, seemly remembering his promise to Ginny (about raising Bonney well). There's more to Kuma's current condition than Oda is letting us know. During the flashback, Vegapunk explained the procedure on his brain had two objectives: erase his memories, and erase his personality. It seems this was partially undone when the kill switch was activated, and Kuma's mind regenerated enough to allow him free will and some sort of instinctive memory. I feel inserting his memories back (by extracting them from Bonney) is the key to fully restore his mind (though there could still be mental scars).
I also feel Kuma's survival against all odds binds Bonney to him. After 3 years searching for her dad, I don't see her leaving him with someone else to have adventures, unless those travels carried the possibility of restoring him, but I don't see how finding the One Piece, discovering the forbidden history or making Luffy the Pirate King would help with that.
This is very likely to be resolved before we reach Elbaf. Kuma and Bonney will then have their farewell and go spend some quality time together as father and daughter.
Another thing to consider is that Bonney's power and fighting style weren't really developed into something particularly interesting or even new to the crew. Her fighting is very generic and even repetitive, and turning into Nika is something that will only really feel special and flavorful this single time.
