Your message "Mia...Sorry i didn't know where else to put this so you'd be sure to see it, I hope check your messages on DC, I sent you a link " should probably be put on Mia's wall.
Yes, and you can either reply to the comment on your wall or come to the other person's wall to reply. It's nice to keep the one conversation all in one place, but I just wanted to leave you a message so you'd have one! lol