This is going to prevent the representative from being seated. This is why tribes opposed the Indian Citizen Act of 1924 [1] in the first place; they were afraid that giving all Indians citizenship would fundamentally change the nature of their relationship with the US government.
The Cherokee can't have it both ways. They can't have American citizenship—and, thus, representation in Congress in Oklahoma or elsewhere—and an extra delegate of their own. Such exists in New Zealand, but that's explicitly provided for by law, and it's controversial; the New Zealand First Party,[2] which a few years ago held all seven Maori seats,[3] has a policy of wanting to abolish said seats, and no longer runs candidates for them.
[1] https://en.wikipedia.org/wiki/Indian_Citizenship_Act