First of all, the skirt is freaking adorable. Its 1960's secretarial vibe would normally lend itself to a pairing with a sleek button-down or even a bustier. I like that Emma has added super-trendy stripes to the look and, by doing so in the form of a t-shirt, adds a youthful edge.
The blue stripe of the shirt does not match the skirt. And it's cool. It's called 'tonal'. I don't love the sepia/sienna stripe in the shirt, but it acts as a nice, earthy base and works tonally with her hair.
To avoid that sepia washing out her complexion, she has added a turquoise collar necklace. It works well with both blues (more tonal) and looks great with the earth-tone. Plus, it's young and fresh.
As for the shoes: who doesn't love navy and red? The cut of the pump is flattering for her feet and legs and gives the whole look pizazz.
I guess that's just another 'Easy A' (wah-wah) for Emma Stone!