I'm the 3rd wheel

I've noticed recently that my fiance includes his mom in 90% of our plans , it's never really bothered me before because we get on really well. I wouldn't mind but my fiance doesn't ask me, He just announces that she's coming.

We've just had a baby 6 weeks ago and needed a new car, so we bought one Monday night.

She Instantly starts calling us silly and saying we are too impulsive and we should have took her with us. She came with us to collect the car yesterday evening and was really embarrassing me interrogating the salesman and overly exaggerating her interest when he brought out the terms and conditions. Insisting that she could have got us a better deal.

It made me feel so stupid like I need a mom there to help me make my decisions.

She was negative the whole car journey and really snappy with my SO. He's her only child so she's had a hard time with him moving out with me and us getting our own things together and every time I try and politely mention to him that I wanna do stuff alone he gets quite offended and defensive over his mom. It's getting to a really awkward time now because I really just wanna do stuff as a family of 3 but it always seems like she's involved or has an input one way or another.

I love her to pieces and she's a great woman but I feel smothered and like she's still trying to molly-coddle us