お姉さん（おねえさん）— older sister (polite or familiar)
友達 の お姉さん です。
She’s my friend’s older sister.
お姉さんおねえさん
older sister (polite or familiar)
おねえさん
accent [2]In detail
Words
友達tomodachifriend
のno(possession: ’s)
お姉さんoneesanolder sister
ですdesu(polite sentence ending)
Kanji
姉シ・
Use お姉さん politely for someone else’s older sister, or when addressing your own. When speaking about your own older sister to outsiders, 姉 is usual.
Coco-sensei