Do I necessarily need to insert the possessive pronoun *her* in the following sentence or can I just skip it?

> Karen, a person, does X together with (her) friend Juliette.

I see that it's uncommon, but under specific circumstances (the back of a novel, or some kind of summary) this would sound right to me.

I suppose *friend* acts as the person's title here; for I'm pretty sure that it's okay to say *She left the room with Doctor Jake.*

I don't need to say *a doctor* / *her doctor*.

Can *friend* act as such a title?  
Can other words, such as job titles (plumber), act as titles?