Not sure who downvoted you, must be the redditor mentality of "I disagree, must downvote without thinking!" ... Back on topic.
I personally disagree, it ruins the interaction between Nami and Diana which is implied to occur in Nami's lore. While more explanations would be nice, the one that is offered would actually be worse then the present one.
I don't really care about Nami as a character too much so I never took interest in her lore but a better albeit longer explanation could be that she looks towards the league as a way of finding the powerful people on runeterra who would actually know where she might find the stone.