It works well have several users in an Ubuntu desktop system, but the system is not really made to work well with several users logged in and working at the same time. Is the problem that the administrator (you) are logged in remotely, and she is not prompted to mount the USB drive?
Have you given her permission to run sudo? In that case she should be able to run
where x is the drive letter and y is the partition number, for example /dev/sdb1. You can prepare a few directories for her to mount on, if she would need more than one, for example subdirectories of /mnt or subdirectories of /media.
sudo mount -t auto /dev/sdxy /mnt
Are terminal commands an option? If not, we need to find some GUI application doing the same or something similar.