In this photo you can see a popular market. As you can see this is the part of the market where women are. In this photo you can also see how local women dress. Of course you don't have to dress like them. But you do have to select your clothes.
Although Luxor is always hot (especially in summer), you should wear long sleeves and long trousers. This is valid for men and women alike. You will find many tourists with bermuda shorts and female tourists with neckline T-shirts, but I don't think this is the appropriate way to dress in an Islamic country like this.