I have a friend like this too.
I'm the typical size 6/8 mom in Jcrew and Gap and Athleta.
She is model thin, tall, gorgeous and wears all designer brands, mostly in black.
Her clothing is cut beautifully and fits her so well.
We look nothing alike but get along like sisters.
I wouldn't say the "typical" mom is a size 6/8 wearing j crew. More like 12/14 wearing target