Should the top navigation of an e-commerce site be duplicated in the side nav or should that area be reserved for filters only?
When you duplicate information, you make the user look at it twice. This creates some disorientation. You can treat the top categories like tabs then expose their sub-categories at the top portion of your left nav. This has the benefit of encouraging subcategory discovery and providing a sense of place within the taxonomy. In a sense, they are the highest order filters of the parent category.
Filter controls are not critical for all ecomm, but fashion shoppers tend rely on them more than most. With that in mind, keep subcategory lists short ('view more' to expand lesser categories can help) so the filters gain exposure to capture more interaction. It may seem obvious, but keep in mind that users who filter typically convert higher.