Next time: Your husband (not you -- your husband, her son) lets her know well in advance: "Mom, we want Child to have a birthday dinner with you, so we're taking you and Child(ren) out to Child's favorite place on Date X! It's going to be so grown-up and exciting for Child to eat there with you and that's the time to bring any presents. We know you don't want to be around all those little kids!"
Then have a separate kid-friend birthday party and don't invite mom.
Sorry, she will complain and accuse you of all sorts of things. But you smile and smile and don't cave. Enjoy the kid party, which you clearly cannot do right now with her hovering. If she bit>>es through the dinner out, smile and ignore. She is getting her kicks out of criticizing you, so do what you want to do your own way and do not reward her with any reactions.Just keep up the line that it's Extra Special To Go Out With Grandma. Your husband, who needs to man up, by the way, should do exactly the same. No explanations, no excuses, just a consistent line of "We want you to have a special time with Child and the kids' party is going to be packed with loud kids."
She may even turn up at the kids' party if it's at your house. So hold it somewhere obnoxious to her (Chuck E. Cheese?) or put her to work immediately when she gets there, refilling drinks in the kitchen or slicing cake IN THE KITCHEN. She will really hate it, and you.
But why try to please her? Enjoy your kids and forget her.
Seriously, it sounds as if (1) she lives too close to you for comfort, no? and (2) you put too much emotional investment into your kids' birthday parties. I would ramp back, frankly, and invite a few close friends over to a "birthday play date" where you have a low-key play time, some cake, and that's it -- no themes or giant cakes or invitations to grandma or anyone else, frankly.
And above all, your HUSBAND should be stepping in and spiriting mom away from you the moment she launches into what you should have served, or any other criticisms. Tell him flat out that he needs to get involved and cut her off. Every time.