Hmmm...That's to bad.
If i were in your shoes i would call her (MIL). And discretly tell her that you do not wish to have a party that is clearly not in your taste, and remind her that it is for you and the baby. ( not her)
And if she does not like it or does not comply with the idea and still insists on hers i will also tell her that you only want one party and a party with all of YOUR close friends.
I hope i helped in any way.