Don't have a good solution for you.

If all flights you want still have space (or if you can change to another flight), maybe rebook and re-ticket in your fiancée's maiden name. AY might be able to coordinate with some airlines to release space, but not all (e. g., JL will not I believe). You will have to find a very resourceful AY agent. Perhaps you will have to pay refund penalty, or perhaps AY can waive it for you. I would not risk all airlines and all airports involved in this trip to let your fiancée travel. Some might let you go, but it only takes one to ruin your trip. Best to change passport name after trip completion, if possible.