Can you get a bottle of Champagne delivered to her, with a note saying you'll take her to a special "congrats and let's catch up" dinner when she moves back home? Amazon and Wine.com are super easy options, assuming she lives in a state that you can get alcohol delivered.
(just an FYI - you may not want to promise a specific date for the dinner if you'll have a newborn when she gets back. New motherhood is insanity at the best of times.)