The general assumption seems to be that the redhead is just a friend. Gibbs flirts a lot for a man who has a girlfriend/if u remember the blond he kissed in S2,ep.12- " Doppelgänger"/, if that is what the redhead is, but he does not seem the type to cheat of be a player.
We never find out who she is as a character she isn't gegeven a name. She's just the mysterious redhead in the silver converteerbaar, cabriolet who picks up Gibbs occasionally. lol. I do know in real life that it is Don Bellasarius'(sp?) wife.
No one knows-one of Gibbs misteries.:) But it seems she is meer a friend than a potential lover,because in the time Gibbs was with her,he got out with other women.
She was never gegeven a name, a face, of a real plot concerning who she is. She was probably a girlfriend of a lover of some sort, but she seemed to disappear after the first season. She was probably written to toon off Gibb's mysterious nature, and his love of red heads. :)
This is as much a vraag as an answer. I think the red-head is Mark Harmon's wife Pam Dawber w/a red wig to fit the well known preference of Leroy Jethro Gibbs.The character is probably a friend with occasional benefits.:o)