Officer Cybil Bennett's police uniform consists out of a pair of strangely tight black leather pants, tucked in her black leather biker boots.
Her shirt is turquoise with two pockets on the chest, short sleeves and - most probably - the Brahms Police Department patch on the sides of the sleeves. In the
Silent Hill 1 graphics you can't really make out what exactly is on there though so you can just be creative
or use the one from the movie as reference for the patches. She is also wearing some sort of badge above her left chest pocket.

Cybil wears black leather gloves with her uniform and
a black holster for her gun which is - opposed to the artwork here - on her right side.

Her hair is short and lightblond. While driving her motorcycle she protects her eyes with big sunglasses which might be a nice accessory for your costume.