She Gets a Kickback
Some decorators have special relationships with flooring, fabric and paint vendors and get a discount for using their products. The key question to ask here is if your decorator is willing to pass along those savings to you!
A decorator could very well charge the full amount, if not more, on those items. This allows the decorator to turn a hefty profit just by using specific products, let alone the fees you're paying her. Some decorators will continually use their preferred vendors because they can make more money from them, not necessarily because the products are the best choice for the client. Be mindful of this and ask your decorator if she's willing to allow you to benefit from any savings that get passed to her. Or, provide her with a list of your own preferred vendors.