She's BORING.
She never does anything remotly intresting.
WoK: Kaldain and Dalinar have multiple fights, taking on dozens on enemies at once, running a bridge towards a flock of incoming arrows while Shallan eats jam.
WoR: Kaladin 2 vs 4's shardbearers, and 1 vs 1's Szeth, Dalinar is on the verge of discovering the game that Odium is playing behind the scenes. Meanwhile Shallan sneaks around at night giving people money.
OB: Dalinar didn't actually do much until the end, but that climax is the best written in fantasy, kill me. Kaladin fights off Yelig-nar, a being with all ten surges bonded to a man we've hated since book one. Shallan spends all book in a downward spiral, accomplishing nothing.
RoW: Kaladin singlehandedly is saving Urithiru, Dalinar is mostly absent, and Shallan is sitting in a box looking at people's faces. And this is where Shallan is best.