The tilt does seem to add to the over-all composition, as it brings her head more into the frame, giving it closer to a rule-of-thirds balance with the bottom of her dress. Her stance has her feet close together, so it seems she might fall over from gravity.
The lighting from overhead, seems it was not full on direct sunlight, since it seems a cloud was partially obscuring the sun, which did help make it less harsh. Good timing! It made the texture of the dress come out very nicely, especially on the ruffles trim. Unfortunately, the light on her face and left leg needed some fill-light. A silver reflector aimed at her face and another on her leg would have been a great solution, or having your cosplayer look up toward the sun would get more light on her face. I recommend a profile of her face, so we don't look up her nose.
If you can't frame out the people and cars, etc, using the Photoshop Clone Tool could make them disappear.
Below is my next submission. I did a low angle, so no horizon and no people in the background are seen. I like how the tilt made the lines of the building, her body, and her weapon become interesting diagonals.