In this scene, Tilly dresses as a schoolgirl and takes a shower!
First off, she wets her tights and the front of her dress before standing under the shower in her hat! She realises that there's not much point to that, so she fills her hat with water before putting it back on her head. She then takes her hat off entirely and stands right under the water!
Next she shampoos her hair and lathers up her body. She leaves the lather on for a while and then washes off and gets ready to head back to class!