So with Dark Fea, her dopplegangers have exact stats as the champions  you use. However, you will always get the first turn, like in other content. By far the most common and effective methods are either; 

1) Use a TM Booster/TM Decreaser and/or INC SPD Champion to go first. This will enable your second turn which can be followed by another TM/SPD CHampion to further boost TM or INC SPD if not done so already, Followed by your DPS. The idea here is to use Glass cannons that hit hard so you will be able to Wipe Her entire team on your first Turn. 

2) Similar to above method; however you will be using a TM booster/INC SPD champ to go first, or just simply using a CC Champion with the highest speed go first to lockout her team.

At floor 90, and especially the final boss, You will be fighting manually for what seems like forever, and she will continue to revive her minions. At this point, you may have to change your champions around a little, for me I have to use a team of strictly all High DPS Champs that are baseline squishy, in order to beat the Final Floor.

*Certain effect Accessories like Reaction Accessories or Revenge Accessories (Change critical hit into normal when attacked before first turn, & 5% chance to counterattack when hit) Do not seem to be replicated by Dark Fea and her minions. I could be wrong, but I have never noticed the effects Proc'ing in any fight, ever.

With this I'll let you decide on champion selection, as you already have some of the  most META champs to use for Dark Fae anyway. Good luck.

You need squishy damage dealers, recovery opption and tm control. allure would be opppttimal, but armiger will have to do for tm control.

Arbiter lead, yur debuuffer needs to go second, that can be Serris, Tayrel or Ghostborn. If Tayrel is booked i woould recommend him as he also has a chance to reduce turn meter. Ninja as you nuker and he should have at elast the cooldowns booked. Last spot Armiger or Geomancer.

Make sure you have all skills available whn facing Fae. Arbiter boost and buff into serris/Tayrel debuff into Ninja frost nuke shold take care of the miror team. Then Ninja hailburn and tm reduction duty for armiger and Tayrel

Play it...and use ninja to freeze the bombs for half damage.  Wrong affinity, but works enough...may take a few times. Don't worry about resistance.  Can kill him if get bomb damage down from freeze.  Must aim at bombs.  and if use Scyl of drakes, which you should...try to use her AoE when no bombs out and then target the bombs with her because decreasing the turn meter would spawn more bombs.  Also use doompriest...and do whoever you want for last two that don't cast buffs or debuffs at wrong time.

Dark Fae is easy, just use an arena team with CC.  So basically make Ninja the fast one and freeze the team.

Thanks