Round 1: Even taking into account the relative equality that being so strong in the Power gives the Forsaken in a fight to the death, Lanfear is very mentally unbalanced, and I think she'd be willing to pull out powers and skills that would not be easily defended against. If Graendal got the drop on Lanfear, though, she'd win - she beat Cyndane and Moghedien when taken by surprise herself, so I think the Forsaken females are more powerful in sheer capability than the males.

Round 2: both are shielded, total catfight: Lanfear is crazy enough to skin Graendal with her bare hands, whereas Graendal likes to give orders and watch others carry them out.