She gazed out the window with her chin resting on her hand, deep in thought.
Tips
culture
A classic pose in Chinese painting and photography for someone deep in thought, daydreaming, or wistful. The closely related 沉思托腮 ('thinking with chin in hand') echoes Rodin's Thinker - Chinese essay writers often invoke the gesture for the same contemplative effect.
memory
托 (to hold up / prop up, like a tray) + 腮 (cheek). Your hand becomes a tray for your face.