Bueller here
I think what you're looking for is what I do with my wife, and between my wife and my mom.
Create a new google calendar and name it something appropriate. Then in the settings>Calendars tab click on the Calendar name you created. Then click on the share this calendar tab. Enter the email address of the person you want to share with (gmail is the easiest), and give them the Make changes and manage sharing permission, then save. They will be sent an invite.
Now both of you will see that calendar along with the calender they already had. You will see your and the new one, she will see hers and the new one. Both can add, edit, delete schedules, reminders, appointments and so forth.
I have four calenders, two for me, one between my wife and I, and one between my wife, my mom, and I. The family is always up to date with pertinent information.
Now my wife and I have droids (Moto for me, eris for her) and the calendars are automatically synced, so ANY changes made to the calendars via the phone or the PC, gets synced to the other objects.
It works great.
Hope this helps