My mother still hasn't mailed my wedding dress, What should I do?

This problem isn’t particularly about the dress being mailed, but that my mother was supposed to complete this task (the only thing I have asked for the wedding) since October. I needed my wedding dress to be mailed to me overseas in order to be altered. I routinely have called and stressed to her that I needed the dress by March. Two weeks ago I called and she told me she was mailing it that day. I called today and after her b/s’ing me to delay the inevitable question, she told me she still had not mailed my dress. Now it is too late to be mailed and I risk not being able to have it altered once I get home in May in time for my wedding. I happened to have access to a dress similar to mine and a size smaller which I have tried on and it fits so I think my dress is fine, but what do I do about my Mom? I am very disappointed and feel let down, my whole life it seems it has been this way.