Y'know what Xanthe could probably do better than anyone else, too, is have Tony introduce Gibbs to BDSM.

*mentally runs through Xanthe fics*

Don't think I've seen her do that yet. Still sub!Tony/Dom!Gibbs, but have Gibbs be a complete novice (with most of his limited info picked up in bits and pieces from Abby or through cases) and Tony having been burned by a previous dom... but completely unable to resist Gibbs no matter how much he wishes he could.