Do you mean to make her manga appearance match the in-game one? From what I've seen of the Super Mario-kun manga, they often steer towards more humourous and wacky iterations of the Mario games, with a more exaggerated cartoony style to match.

Seeing as Tippi's initial personality is more reserved and straightforward in the game, she wouldn't offer much in creating humour or adding to the antics of Mario and Co, so they probably changed her personality to be more cheerful and upbeat to bounce off the other characters better. This then extends to her design, with a face allowing for more fun in images and reactions and fitting the manga's overall style more.

TL;DR: Mario-kun plays fast and loose with the games already, so they take liberations to better suit the humourous and wacky style of the manga rather than be direct adaptions.

She's a ghost in an artificial body, they wanted her (and the other Pixls) to be more alien