Couple of good ways that I have employed in the past: Send update letters (even if it's just a note that you're still shadowing/working in a clinic/working in a lab/volunteering as you have been) to Calloway directly as an email attachment; send a short email letting her know that you're still interested, ask if there's anything you can do to improve your status on the waitlist (even though there usually isn't), and be direct that you're writing her so that your name is in the forefront of her mind when she's making further decisions regarding who to accept off the wait list.
My suggestion is to avoid being coy or cheesy about the emails... remember that she's probably getting dozens per day. Be honest about your intentions. It helps if you stopped by her office after your interview and met her personally---easiest way to plug yourself. If not, don't be shy, it's time to pull out all the stops and swallow all pride. I know it's hard (I've done a whole lot of it myself).
Also, if there was some part of your application that was weak (i.e. MCAT, like me) it's a good idea to let her know that you have specific plans for enhancing that item (Your plan is to go ahead and retake the MCAT this summer) which will help show your determination to keep plugging away.
Good luck. Hope this helps. If there's anything else I can do, I'd be glad to help. This is my third time applying, so I know your pain.
Is it better to address her as Dr. Calloway or her rank?