She's not his friend, she's mine
Robert didn't drink his own coffee. He drank hers

That is one of  her friends. 

His neighborhood is safe, while my neighborhood isn't. 

His neighborhood is safe, while mine isn't. 

Did your mother call? 

I don't know  them very well. 

I don't know  their daughter very well. 

I talked to  my grandmother for three hours last night. 

I think I got my notes mixed up with  yours