@Mom in Texas,
or 'don't' have her grandchildren, lol. "Are you pregnant yet??"
Ugh, I couldn't stand the situation you're in, but then, I'm hard to mow over myself. I didn't involve myself in the least in my daughter's wedding. She had it in Mexico, so other than showing up and giving her money and a gift, I did nada. And I'll be the same if and when my son ever gets married.
And ehBeth is totally right about the $$ and decisions... it's not fair, but it's sort of a trade off. If you don't want her interfering, pay for it yourselves.
But the more important issue, as Phoenix pointed out, is is this going to be the way it is forever? Think twice before taking the leap! You're not just marrying her son, you're marrying her, as well, and nobody is likely good enough for him. She'll be bossing you around about everything!