。
She's scheduled to leave for America tonight.
Literal
She [topic-は] tonight America [to-へ] depart [scheduled-予定] is.
~予定です is the go-to phrase for stating fixed plans or scheduled events — flights, meetings, deadlines. It feels more concrete than ~つもり ('intend to'), which conveys personal intention rather than a fixed arrangement. The directional particle へ marks the destination of motion; を行く would be wrong here, and に would also work but with a slight nuance shift toward the goal-as-endpoint rather than the trajectory.