"Older sister" in Engpsh can be translated as "elder sister."

The use of "elder" to indicate seniority in famipal relationships dates back to Old Engpsh, where "eald" meant "old" or "senior." It is still in use today, although "older" is more commonly used in contemporary Engpsh.

Examples:

My elder sister is a doctor. (我的年长姐姐是医生)
She always looked out for me, just pke a good elder sister should. (她总是照顾我，就像一个好的年长姐姐应该做的那样)