Looking at the costume, you can tell it's Supergirl. I was really surprised they went with the classic skirt look. I assumed that they would go with the one piece swimsuit look of the current comic book design. Colleen Atwood, who designed the suits for (Green) Arrow and The Flash, did a very nice job with staying true to the original suit. My only quaims are the leggings and the tall boots, but it's minor at best.
Here's a photo of Benoist as Supergirl. It's great that she's got her hands on her hips, looking very much like her more famous cousin. I Photoshopped her smile over the frown, and played with the saturation levels until you could actually see some colors.
Sigh, it just seems too good to be true.