This is a very good question. I'm sorry it took me so long to answer, but I've actually had to think about the answer for a long time.
Public relations is all about your relationship between you and your target audience. It intersects a lot with marketing because of the publicity function of public relations, but PR engages in a different set of tactics than marketing does. PR engages in Media relations, investor relations and consumer relations. PR practitioners hold focus groups within their target audiences, they listen to feedback provided by their audiences and they communicate back (either face-to-face or through some other medium).
Public relations professionals manage the relationships between the client (ISA) and its target audiences (Int. Students, Domestic Students, Int. Affairs, Oregon Hall, ect.). They make sure that these audiences have a good and healthy perception of the client AND make sure the audiences know about the clients events.
I'm sorry if this is still convoluted. If it helps, this is a difficult thing for PR students to understand too, and I'm also still not 100% sure what exactly it is that separates PR from Marketing. But I hope this helps a bit.
—Bryan
