You can see that the shoulders are exposed; look at her right sleeve in that image. There's a lot more wrong than that, though:
- Hood doesn't come all the way over the front of the head, which would leave hair exposed to get wet and drip onto the face
- Hood's wide-open, baggy cheeks would collect water and/or funnel it towards the neck
- Shoulder cutouts would allow water infiltration to arms and torso
- Short yet wide skirt would leave underclothes all but unprotected from splashing
- Completely exposed and unprotected kneehighs would get soaked and wick that moisture down towards the feet
- Relatively low-cut yet widely flared boots would constantly collect water
All in all, a terribly ineffective design for jumping around in the rain. I didn't mind in the episode, because it was pretty cute, but I couldn't believe they had the nerve to describe it as "fully waterproof" afterwards.
Image unrelated by the way, I just like Chiharu.