Brie is promoting Unicorn Store, which she directed — and interestingly, she auditioned for this five years ago but didn’t get the part, and then grabbed it to direct when it came back around and she was looking for an opportunity. The LA Times says she “decided” to play the lead but made a point of casting an unknown in a crucial role to try and give someone a leg up; I read that as, “No one would let her make it unless she starred in it, because she has an Oscar now.” (That’s not an insult, by the way. That’s how the sausage gets made. I’d be willing to bet “starring Academy Award winner Brie Larson” was the prerequisite that enabled her do it, and why NOT take advantage of that for a script you already love?)
Regardless: The movie, in which Samuel L. Jackson basically tells her she can get a unicorn if she follows his instructions — so, yeah, mega-quirk — explains some of her outfits. At LEAST one of them, anyway.
Spoiler: It’s not the first glittery pair of shoes you’ll see. (She looks adorable in that. It’s Carven.)