She also wanted to sail the seas you know.
The entire theme about being free. Many people already foresaw her joining.
I was 50/50.
It can go along with the sign of a possible recruit in Luffy helping the recruit out from being stuck and giving them freedom:
Untying Zoro from his ropes.
Getting Nami out of Arlong’s corrupt money deal and torment.
Helping Usopp break through his fears.
Helping Sanji realize he doesn’t need to stay with Zeff to help him out even though he saved his life.
Convincing Chopper he doesn’t need to hide himself away on a winter island from people who might get scared of him being a blue nose reindeer monster.
Carrying Robin out from being trapped and buried in the Alabasta tomb.
Helping Franky realize he doesn’t need to stay on Water 7 fighting criminals and atoning for his actions for Tom’s sake.
Getting Brook his shadow back so that he doesn’t stay trapped in the darkness.
Breaking Jinbe out of prison.
And I suppose Luffy removing Yamato’s handcuffs could fall into this idea as well.