She is very calm.

Literal

She [topic-は] very calm.

穏やか ('calm, gentle, mild') is a na-adjective often applied to people, weather, and the sea — anything that can be unagitated. About a person it suggests a serene, even-tempered disposition. About the weather, 穏やかな天気 means mild and settled. The character 穏 itself carries the radical 禾 (rice plant) on the left, suggesting tranquility tied to settled agricultural life.