Both of you create Apple ID's. The App Store and Music store will use one Apple ID for purchases so you can share.
Sign into iCloud using your Apple ID, check all the boxes that you want on your iPhone. Now add her iCloud account with her Apple ID but only turn the Calenders on.
Repeat on her iPhone but using her iCloud as primary, and your iCloud just checking the Calenders.
That way you will both have your own calenders, but you can see each others. Her appointments will be one color, yours another.