YOU SAID:

i just came back from the party, where I saw my sister's friend

INTO JAPANESE

パーティーから帰ってきたところ、妹の友達に会いました

BACK INTO ENGLISH

I came home from a party and met my sister's friend.

INTO JAPANESE

私はパーティーから帰ってきて、妹の友達に会った。

BACK INTO ENGLISH

I came home from a party and met my sister's friends.

INTO JAPANESE

私はパーティーから帰ってきて、妹の友達に会った。

BACK INTO ENGLISH

I came home from a party and met my sister's friends.