Oh, I bet she's shy around you. Either cowed into near silence by your overbearing, overwhelming, overweening selfishness and megalomania or she is too biting her tongue nearly in two to stop herself putting you firmly in your place to dare say much. Either way, you are awful!
Not like she'd be entertaining people? Erm, as you seem to have forgotten, SHE is the mother of the child who would be the focus of the party (well, I know you want to be the focus, but you'll be disappointed). People will naturally flock to her and want to talk to her, ask her things, pay her compliments, try to get gory details, offer unwanted advice... the whole gamut of conversation you have to deal with as a new mother. I know that in your mind, this party will consist of you wafting about looking maaahvellous, holding your grandaughter in your arms like some radiant mature madonna, as everyone else compliments you on your amazing skills as a grandmother, blahblahblah, but it ain't going to happen.
As for your son and partner not having a car so they 'had' to accompany you: have you heard of such a thing as public transport? Taxis? Bullshit was coming with you the only way to get there. Hell, if you were that worried about them meeting their new niece, you could've given them a lift.
It's very nice that your in-laws had a say and certain rights in your childrens' lives. BUT THAT IS NOT NOW. Just because you did it one way does not mean it's going to happen now.
You sound incredibly controlling. Cntrolling to the point of it almost being a personality disorder or mental health issue. You are blaming these non-problems on your DIL, but has it occured to you that it's all from your son finally finding his balls and usijg this excellent and apt opportunity to try to get you to grasp the message that things aren't all about you and to back the fuck off. He is not some glovepuppet mouthing the things your DIL insists he tells you. He obviously feels passionately about keeping this special, unique time for him and his wife between them and good for him. At least one thing I can say positively to you is that you must have done something right to have a son so loyal to his wife.
I really do believe that how you have been acting and probably have always acted, is actually making them hold you more at arm's length than they would do if you weren't so determined to decide what's right for theothers in your life and obsessed with asserting your own needs and rights - rights as you see them, that is.
The one person in all of this that you seem to have not thought about once is this lovely little girl you profess to care so much about. This is a time where she needs to bond with her mother and just be with her, and her Daddy to a slightly lesser extent. She doesn't want or need to meet what are strangers to her, she doesn't need her mother stressed and insulted whilst they bond and connect, and she certainly doesn't need a party. If you really love her, you would support her mother. Which is not you, in case you'd forgotten.