Wait, since when US want exclusive citezenship? Never heard about it.I'd just chalk it up to Pippa confusing green card with citizenship.
IIRC she went to a UC and works for a CJ/Samsung subsidiary as manager-level. No way she's illegal, and probably already has PR (to qualify for UC residency requirements).
She probably doesn't want to naturalize into US citizenship because she'd have to give up Korean citizenship (too HAG to qualify for dual).