My God, yes and my God is in church so you can already see I am bias. I can go on and on about this because I just got married last year and there is always a grudge in my stomach because I didn't do it all for ourselves. It was my parents' party. The first I am saying to you is, DO IT FOR YOURSELVES!!!! I know you want harmony in your special day, you want everyone to be happy, BUT how about you? YOu have to be happy yourself. You have already pushed it to 2007 (my parents picked the day too) for your MIL, don't do anything for her anymore. If it's important for you and your parents to get (your) God's blessing on your marriage, do it!!! If she refuses to come, explain to her that she picked the year for her God, now you'd like to something for yourself and receive blessing from your God (Jess, I believe there is only one God. But I grew up with the mixture!). If she still can't see it then tell her you both would love to have her there for the ceremony but you understand if she can't attend due to her religion, then she can join after the ceremony. Her son should talk to her as well, it's not her wedding. Don't do this for anyone, you will regret it, do exactly how you'd like YOUR wedding to be! Take my words for it! At one point I was so sick of listening to people I started snapping at people...YES became a bridzilla myself... :embarasse shame!
And as I said I grew up with the mixture of Christian and budhist, I am telling you a real budhist is more forgiving, open and loving then being stubborn and pushy and bossy. Buddha will tell your MIL harmony with people and with one's own heart is more desirable therefore let people do what makes them achieve harmony within themselves. Am I making sense here? Just my 2-cent, hope I am helping a little.
K.