While T'Prynn is described as being statuesque in the novel, I have to say that picturing the smaller-framed Amy Acker works better for me, because it, to my mind, almost serves as an ironic commentary on the nature of the character in terms of the difference between appearances and actual nature -- T'Pyrnn seems
to be a cold and logical Vulcan but is actually a deeply emotional, troubled woman, and so the idea of her seeming
to be small and relatively weak-looking but actually being (due to her Vulcan physiology) a very strong, very powerful person works for me as an extension of the ironic duality of the character.
Well, that and I really have the hots for Amy Acker.
For what it's worth, though, I'm definitely picturing Amy Acker in Illyria-mode, not Fred-mode.