。
She smiled at her reflection in the mirror.
Literal
She [topic-は] mirror [in-に] reflected self [to-に] smiled-at.
Two interesting bits. に映る ('be reflected in') uses the verb 映る ('to be reflected, projected') with に marking the surface of reflection — 鏡に映る ('reflected in the mirror'), 水面に映る ('reflected on the water'). The past-tense 映った serves as a relative-clause modifier of 自分: 鏡に映った自分 ('the self that was reflected in the mirror'). Then 笑いかける ('smile at') is a compound verb that uses ~かける to direct an action toward a target — the reflected self.