Who is my Supervisor's Administrative Assistant?

You can expect your supervisor's administrative assistant to be a resource for helping you navigate things like reimbursement requests, dealing with administrative problems outside Student Services or academic matters, ordering stuff for the lab, etc.  Generally the Admin Assistant will prepare documents for reimbursement with the exception of Travel (which you do yourself through Concur) but can also be a source of help for Concur.  What you should not expect is that the do things for you.  They work for the Professor, and are there to help, but they do not have the time to prepare travel reports for every student, for example.