Step one of Dora's plan--the plan to get her out of the confining walls of Hogwarts, out of the library and out of her common room and dorm--was to go outside. She had, of course, been outside during the duration of her six years at Hogwarts--she did have to attend the mandatory flying class first year, after all--but she had not been outside very much for her own pleasure. If one didn't know any better--and if her skin hadn't been naturally tan--Dora could have been mistaken for a person allergic to the sun.
In order to carry out step one Dora had to collect the necessary items. A blanket, perhaps, to sit on, a book to read so that she had something to do. She wished for company, wanted to make friends, but as none were readily available at the snap of her fingers--or ever, for that matter--Dora made due with a book, while in the meantime hoping someone would approach her for conversation. Sunglasses, muggle by nature and a necessary item in her mother's mind, were the finishing touch. She was wearing her school robes, and while in the castle the remained closed and buttoned, hiding the fact that underneath she wore an outfit from her muggle life--a flippy skirt that hit at her knees in a shade of white only appropriate for spring and a rose-y pink blouse with a modest v-neck. While she tended to follow the rules to a letter, Dora figured that since classes were over for the day and she was on her own time currently, she could wear what she liked.
Having all the necessary items, Dora exited Gryffindor tower and headed to the lake. Once there she made herself comfortable near the edge, in the open, where she hoped a few feeble rays of sun might catch her.