Codex: Imperial Agents offers us a special detachment for Adepta Sororitas called Vestal Task Force to play around with.
This formation seems to be only exclusive to this book and can't be used with units from the digital only codex. At least I believe so since this book does move things around a little bit. Most notably is the elite choices in this book are just all of the new force org units, besides the Ministorum Priest who is now an HQ option.
Crusaders, Deathcult Assassins, Arco-flagellants, and the Sororitas Command Squad are elite choices now.
Your compulsory's are 1 HQ, 2 Troops, and 1 Elite unit, with your optional's being 1 HQ 4 Troops, 2 Elites, 3 Fast Attack, and 3 Heavy Support units.
The Restriction is quite simple, all your units from this Detachment must have the Adepta Sororitas Faction.
Army of Faith: Once per game, at the start of any of your turns, you can declare that the units in this Detachment will pray for salvation. If you do so, then all units from this Detachment can re-roll any saving throws of 1 until the start of your next turn.
Blessed Warrior: If this Detachment is your Primary Detachment, you can re-roll the result when rolling on the Adepta Sororitas Warlord Traits table.
All and all pretty decent, for one turn you get a better mark of Tzeench but at the cost of an elite slot.