She is always very even-tempered.
彼女はいつも情緒がとても安定している。 - Weblio Email例文集
He has an even temper―a smooth temper―an equable disposition―He is an even-tempered man―remarkable for his equanimity.
彼はいつも心の平らな人だ - 斎藤和英大辞典
acting in a manner that is gentle and mild and even-tempered 優しくて温和で冷静な態度で、行動すること - 日本語WordNet
Third, given that Yamato means to become more even-tempered, I intend to help archers with an inflated sense of their own abilities and who don't understand the truth of Kudo to see reason.
三には、愚かなる射手弓道の術理を弁へず、邪儀慢心なる夷心を大に和ぐとの道理を以て、大和流と号する也。」 - Wikipedia日英京都関連文書対訳コーパス