Hmmm.  Can you give me some details about what's been going on?  Who is your sister?  What kind of friend is this?  And what sort of advice did you want to give?
assistant
Oh wow, that sounds like a difficult situation.  How much have you told your sister about how her friend has been negatively impacting you?
assistant
How do I advise my little sister that her friend is a toxic person?
user