Sister-in-law: the spouse's older sister or the wife of one's older brother (a non-blood older sister by marriage).
義姉（ぎし）は料理が上手で、よく教えてくれる。
My sister-in-law (gishi) is good at cooking and often teaches me.
週末は義姉と買い物に行く予定だ。
I'm going shopping with my sister-in-law this weekend.
彼女は夫の義姉にあたる。
She is his wife's sister-in-law.
Older stepsister/adopted older sister: a non-blood-related older sister (e.g., from remarriage or adoption).
義姉は私が引っ越すときに家具を手伝ってくれた。
My stepsister helped me move my furniture when I moved.
養姉がいるため、血のつながらない姉妹関係に慣れている。
Because I have an adopted older sister, I'm used to a non-blood sister relationship.