I put in my wife's email. She accepted the friend request. It's been an hour, and I still can't purchase a ticket for her. 

How long does it take for system to update?

Did you try logging out and back in again?  Sometimes that helps things update.  

What's worked for me: I've added the friend, the friend confirmed it, then had the friend add me, then I confirmed it.  Kind of a convoluted process, but it did the trick.