Pushy, Controlling MIL!!

I'm sorry but I've attempted to bite my tongue! 
But come on she's bought the baby a BIKE!!!! 
He's not even born yet!! That is something I would want to buy my son, but when the time is right. 
Ofcourse I had never told her not to buy a bike! He's not even here! 
I feel important purchases like that are for a mother to buy or to atleast have a say in. 
This isn't the first time she's tried to take over the decorating of his nursery too. 
It's really getting me down and I can't talk to her about it because then my partner gets upset with me!