My suggestion would be to base your list on the Craftworld Eldar Codex to give you access to things that the Dark Eldar list won't have. Since your fiancee is playing Dark Eldar, if you want to supplement them with a nice fluffy Harlequin list, I would suggest having her focus her list on speed and shooting, and focusing your Harlequin list on hard-hitting close combat (since that is what they are really known for).
I recommend the following as fluffy Craftworld units to use as Harlequins:
HQ:
Use the Autarch as a Great Harlequin - kit him out in whatever way suits you. His shield will help to represent his Holo-field
An Autarch kitted out with the Mantle of the Laughing god could also make a serviceable Solitaire (since he won't be able to join units, but gains Hit and Run, +3 to Cover Saves and re-rolls failed cover saves, he becomes very survivable - for a single character that is.
(Sadly, the best Solitaire is found in Codex Dark Eldar - Lelith Hesparax is absolutely PERFECT as a Solitaire - but the Craftworld kin seem to have the best overall for the theme - thanks especially to the Warlocks as noted below.
TROOPS:
Windrider Jetbikes w/ Warlock (choose the Conceal/Reveal option and keep them Concealed for a fluffy Holo-field-esque save that adds nicely to their Jink for up to a 2+)
Storm Guardians w/ Warlock as a Harlequin Chorus (again, choose Conceal/Reveal to keep the holo-field theme)
Rangers - can be tossed in just to add a bit of shooting or fill a Troops slot if you don't like the above two.
ELITES:
Harlequins are the obvious choice here - kit them out for full fluff-friendliness.
FAST ATTACK:
Shining Spears could be nice as Harlequin Jetbikes if you don't go the Troops route for them.
Swooping Hawks can be used as a unit with more powerful Flip Belts that allow them closer to true flight. (In my home-brew Harlequin Codex, I have a unit like this called Wind Dancers which I use as close-ranged fire support and mobile harassment, and specifically set up to use as Swooping Hawks when I have to go "counts as" style.)
Avoid the temptation to bring in a flyer - they don't fit with Harlequins. Let the Dark Eldar bring theirs if you feel the need.
HEAVY SUPPORT
Dark Reapers can make a serviceable Death Jester missile team.
The Wraithlord can make a nice centerpiece model for a Harlequin force - just make sure it has a Ghostglaive for close combat, and maybe get a flamer or two for more up-close work to keep to the theme. (Harlequins had "Eldar Dreadnoughts" in their list back in the day, though a lot of use home-brew types have taken to calling them "Marionettes" these days.)
