I understand totally why you are pissed off.
If someone tells you they would like to take you shopping and buy something for you, then they are buying something of your choosing.
Or they just go out and get you something!!!
To say no, that's horrible, is stupid. She's not buying it for HER, she doesn't have to like it!
However, you have really come out on the attack here. AIBU is where you ask if you are being unreasonable.
You clearly don't think you are, so perhaps relationships, or chat, would have been a better place for a rant.
You asked for opinions. I am not having a go at you, because you're cross and personally, I can see why. But coming on here and launching yourself at people who disagree with you is not going to end well for you and is only going to wind you up even more.
You don't want to be fighting on 2 fronts.
And, much as I too think your mil was being bloody rude, you would be better served by taking a deep breath and laughing at her (not to her face!
) but have a good old giggle about her insanity. Let it wash over you, not wind you up.