Sending Calendar Invites on Iphone - Need Help

My wife and I both have iphones. I go to calendar and create an event. I want to add her to the event so I go to edit>invites and then go to her name in my phone. At this point it will not allow me to add her to the event.

I notice that once I put in her email, it will allow me add the invite but I want it to go straight to her iphone calendar, not her email.

Any suggestions? Thanks.