Even though the Countess is FI/CI in Hell, that does NOT mean you need a build that contains lightning, not at all. Your Merc tears her apart easily.
Any build can dispose of Pindle and Countess easily with Merc company.
If you choose to have no Merc then CL/FO might be a good idea. Though a Sorceress without a merc is pretty intensive to play since you will teleport alot.