Luna usually shrugs off a lot of less than good-natured teasings, so she'd have no trouble with George's attempts. Who knows, if the jokes are really funny (even if aimed at her) she might give the biggest laugh.
Don't worry, Luna might probably not notice - or she'll merely label Fleur as a bit unkind and move on.
Ha. That would please Luna. Well, not the laughing in private, but you know.