Birnin Zana
Honorary Wakandan
Lupita is younger than Chadwicke breh..
For this to work out she CANT be cast as Monica Lynne PERIOD. She'd have to be an alternative take on an existing Dora Milaje or a brand new Wakandan character.
Even with Boseman already introduced you STILL need to introduce the nation of Wakanda, the central villian, establish Black Panther's power set and the Heart-Shaped herb, and possibly even Bast as a spiritual/mystic entity. Introducing Shuri is crucial, but giving her an entire arc worthy of her character whole T'Challa deals with whatever the crisis turns out to be, PLUS setting up T'Challa's arc within Infinity War (which has been confirmed by Fiege) might be a little more than can be reasonably handled. I'm not saying don't introduce Shuri, I'm saying that her role within the first film will more than likely be smaller than befitting a star like Lupita
No need for a full-fledged story arc. Just do it like Star Wars did Poe: have her doing cool shyt.
Poe's arc was maaad straight forward, but everyone got the point real quick and it worked very well. Just have Shuri as the warrior princess who fights hard for Wakanda in the battle field, banters often with T'challa, and even has a brother-sister moment with him. Give her a clear personality that is reflect of the comic books as well and you're good to go .
She can continue being developed via sequels as well.