While that sucks, I thought it was common knowledge that if you don't show up for the first half of a round trip the airline will cancel the 2nd half. It's unfortunate that the Expedia agent did not give your wife correct information.
You can attempt to appeal to supervisors and what not, but you're fighting an uphill battle. Keep the focus on the death in the family, that you're military, and that had the Expedia person given you proper information you wouldn't be in this situation.
ps: This is why you should only deal directly with the airlines. Once you get a 3rd part involved it's a mess.