They probably didn't even get married, since she's Juliet Carlson. - Edit 1
Before modification by Cannoli at 29/05/2010 03:55:46 AM
She also had a relationship with Jack, presumably, that didn't work out for them because both of them unconsciously wanted to be with other people.
Juliet seems to have a much more amicable ex-relationship with Jack than she had with Edmund, but she kept Edmund's name after the divorce. She worked with both her exes so we can't even suggest she dropped the "Shepherd" name so people in their hospital would not get confused, since she worked not only with Edmund, but directly under him. She & Jack would have been in completely different departments.
IMO, this points to a very brief relationship where she got knocked up and kept the kid. It also explains why Jack has much less custody (one weeked a month IIRC).