I threw a shower for my bff while I was preg and had the same issue. I ended up not getting anything but rudeness from her MIL...she said she'd bring stuff and she didn't and she didn't pay what she said she would either. It was very frustrating but in the end I kept the mom to be focused on the fact that it was her day and no matter what else was going on to stay stress free and enjoy....just had to yell at MIL once lol. Keep focused on the big picture and forget your MIL
..if she pouts and says u didnt include her late r point out the times u tried and she bailed and leave it at that.
It sounds like this may be overwhelming for her. To me, this is too much, and it may feel like that to her, too. If your mom is able to, have her send out your invitations about 3 weeks before the shower, and come down one Saturday so you can go through the venue, and then go to Hobby Lobby and pick out a few things, and invite your MIL to come along.
She sounds like a spaz :( I would just plan the whole thing with my mother and the in law will figure it out when she recieved her invite. :(