Berylla is lean, almost to scrawniness.
Berylla is not particularly strong in the One Power, she was one the weakest in Liandrin's group. Her level of strength is described by "The Wheel of Time Companion" as 27(15) which is a middle level in Aes Sedai hierarchy. With this level of strength she is unable to open alone a suitable gateway to Travel.
She is as fine a manipulator and plotter as there ever was.