I would be totally happy with Johanna being a nobody, or someone unfamiliar.
She's a pretty big role, and has a reversal of relationship with Katniss. Johanna is such a royal pain in the a** when she wants to be

They'll be doing plenty of "over the shoulder" shots with Johanna in that first scene in the elevator. She's stark naked, she's this close *ll* to Peeta. And the book talks about how the lights shine off her chest.
I can't wait. 'Cause there's that moment when Johanna yells about sedition up to the arena's audience, that Katniss' more murderous thoughts are doused.
Johanna and Katniss also bond as they come off morphine, or morphling, as the Capitol calls it. The book gives a nice antidrug message, it's seductions and it's price. Johanna leisurely 'swipping' Katniss' from her arm IV *shakin' head*
*And*, Finnick likes her. Trusts her.
They're already at work on "Catching Fire". WoooooooHOOOOOOOOOOO!