I think Rarity and Twilight would make great friends by the fact they look details and organization. I think ironically Twilight might potentially be the most into fashion despite being more of a wallflower because she can appreciate how a dress can complement a pony. Not as much for status unlike Rarity, but instead just on how it works.
It’s kind of a wasted friendship. I think unlike Dash who used looked down on Twilight’s knowledge until later, Rarity from the beginning would probably appreciate it, respect and even find her knowledge useful.