YOU SAID:

I think the friend of my sister Katherine who’s 10 years older than me is beutyfull

INTO JAPANESE

私より10歳年上の妹のキャサリンの友人はとても美しいと思います

BACK INTO ENGLISH

I think my sister Catherine's friend, who is 10 years older than me, is very beautiful.

INTO JAPANESE

私より 10 歳年上の妹のキャサリンの友人はとても美しいと思います。

BACK INTO ENGLISH

I think my sister Catherine's friend, who is 10 years older than me, is very beautiful.