He needs to first set the access privledges on his calendar to give you
that access. Then you can use the open other user's folder function
from withing Entourage.
Use the File menu and select "Open Other User's Folder". Select "Calendar"
for Type and type in her name and press return. If she has granted you
permission, you will see a new view for her calendar.
An important Exchange server patch needs to be in place in order for all the
sharing to work properly.