AITA for telling my boyfriends mother that she has no say in what height of shoe I wear to her daughters (My best friends) wedding?

I (27F) am 6'6" tall, i've been dating my boyfriend (28M) for four years and living with him for a year, he is 5'7" for context, his entire family is quite short. Despite the height difference he has never been uncomfortable with it like some of my past boyfriends have been and encourages me to wear my favourite shoes. If i'm not working out I tend to wear 6 inch heels as it's just what i'm most comfortable in.

We are going to his sisters (27F) wedding in two months, she is my best friend from Highschool and actually the reason I knew my boyfriend in the first place and is 5'1". She has also never had an issue with my height though has always expressed envy. As her best friend I will be her Maid of Honour.

Their mother has asked me to wear flats to the wedding stating i'd be the tallest one there and stand out too much I annoyed by this as this is the same woman who when me and her daughter were going to prom expressed similar views and told her no one would care how tall I am as I grew up with her daughter and have dated her son for some time the family know me and know i'm tall. I've also met her fiance's side of the family so there will be no surprise there. She told me if I marry her son then I can be as giant as I want but this is her daughters day and she doesn't want her to be literally in my shadow. I finally told her she had no say in what height of shoe I wear to her daughters wedding and that is between me and her.

I did later check with my friend if she wanted me to wear lower heels than I normally would pointing out what her mother had said and she told me not to worry about it and wear whatever shoe I feel comfortable in. I have heard through the family though that my friend and boyfriends mother has been stressing over me being so tall for the wedding throwing out how i'll ruin photos to how i'll tower over the wedding party, even trying to imply that I might be too big for the doorway into the chapel. It's annoying and grating on me but I know it'll be even worse for my friend so I feel guilty over this and being the reason she's having to deal with this drama.

Maybe I should just wear flats but at this point it feels like i'd be caving and setting us down a slippery road and also my friend told me to wear what I want. I still feel maybe i've caused her undue stress by telling her Mother she had no say in this. Am I the asshole?