OMG. I feel your pain. My FMIL is so insistent on what she wants that it seems like it is her wedding. I cant stand it. Its MY wedding!!!! Also she thinks that she can have me all to herself and gets mad when I invite other people. Its so overwhelming.
The only thing I can say is good luck! Maybe when you have the time to go she will be busy or something.
If you think of any other excuses let me know. I may need to use them.