I would tell her that you would be HAPPY to have a hometown reception for them when they got back. She could wear her dress, have a cake, open presents, the whole 9 yards!!!
While she has reduced the costs, it sounds like she hasn't been hearing you at all. Would your husband be willing for you to put the "blame" all on him?? Would that take any guilt off you?
If she keeps calling and bugging you about it - even after you've explained.....I would buy an answering machine/caller ID, install it and then SCREEN YOUR CALLS!!!!!!!!! Don't pick up when you know it's her! Hopefully she'll get the idea.