The most she could do is see if her fiance could deploy at a later time. While not likely, the military isn't completely heartless when it comes to these things. Besides, there is no way either of them could've known during the wedding planning that he would be deployed that day. Don't you guys think they would've changed the date if they knew this earlier? If her fiance can't work something out, then she is out of luck. Depending on how close it is to the wedding, it's really difficult to find a day where everyone and everything would work out like you wanted.
OP, I"m sorry that this is happening to you. I'm a military wife as well, and I couldn't imagine how frustrating and heartbreaking this is.