Man i can't believe how some people still don't understand oda's story.
Whether they truly believe it or not, or use it as a excuse- the emphasis that Yamato and Momonosuke are somehow fated to be together or that she will follow him is simply not true in any sense.
The real reason Oda had Momo interact with Yamato and have them work together during the raid is due to multiple reasons and none of them have anything to do with Yamato wanting to follow Momo.
1. Sweet irony- Orochi who was under the guise of a loyal servant of Oden's father, betrayed their trust after getting the Shogun title from Oden. Yamato- daughter of kaido who was an ally of Orochi at the time of his betrayal, is betrayed by his own daughter and switches sides to the very side he helped in destroying.
2. You are his son, but you are not your father- Yamato is strong like her father, but she doesn't share his desire of wanting her to rule Wano. Momo is royalty like his father Oden, but he does not have the same admiration and raw strength, therefore he must rely on other means to live up to his fathers' expectation and legacy, through humility and perseverance.
3. Future generations will succeed where older generations failed, aka inherited will - Momo will succeed where Oden failed by being the Shogun that Oden never was and couldn't become. Yamato will join the new Pirate King's crew and find the One Piece where Kaido and his old crew and captain failed and could never achieve, namely the Rock's Pirates and Kaido's Beast Pirates. Oden was never a good ruler, but his son will be, clearing Oden's name. Kaido will never reach Laugh Tale and find the One Piece but her daughter will. In this sense, both Oden and Kaido will have their desires fulfilled somewhat, just not by themselves, but by their children.
4. Crossroads of fate- Momo bringing Luffy to Wano allows Yamato to finally meet Ace's brother- giving her the chance to join Luffy's crew and leave Wano, Momo meeting Yamato gave him support in a critical time where neither his father Oden, nor his loyal retainer Kinemon was no longer around to support him in his time of need of finally overthrowing Kaido and claiming the title of Shogun.
So while Yamato and Momo crossed paths and met each other, they walk different paths and have different end goals, therefore they were never meant to walk together.
If you can't understand at least this much, then i can't take seriously your arguments of Yamato joining as Momo's loyal follower and not Luffy's crew.