she is his sister,helen.

she is his sister,helen.
she is his sister,helen.

she is his sister,helen.
她是他的姐姐,海伦.

她是她妹妹/姐姐，海伦

她是他的姐妹，海伦
要明确表达姐姐的话用elder sister,妹妹用younger sister

她是他的姐姐/妹妹,海伦

她是他的姐姐/妹妹，海伦
一般如果要明确表达姐姐的话用elder sister,妹妹用younger sister