I'm so nervous because of that! I emailed Ms. Hewitt and this is what she sent:
"Thank you for your email and interest in our program. Regarding the letter writers, yes, you may have your current supervisor write a letter for you and this will meet the professional letter requirement. I do know that the admissions committee does like to see that you have some shadowing experience with a physician and so a letter can also help to support that. If you have a physician you’ve worked with who is able to write a letter, I suggest including your supervisor’s information as the official professional letter writer, but also request that the physician send in a letter on your behalf.
The letters may certainly come in after the application, we actually don’t match up letters to files until we’ve received and processed applications, so that’s not a problem. Just note, all materials must be received before your application will move into the queue for processing in preparation for review by the admissions committee."
So I don't know what to do!