I found this picture on the net, accompanied by the following text: "This is not the defect of the charming, dusky, white - robed person who, in the Tangerine subject exhibited at the Salon of 1880 [Fumée d'Ambre Gris] (the fruit of an excursion to the African coast at the time of the artist’s visit to Spain), stands on a rug, under a great white Moorish arch, and from out of the shadows of the large drapery, raised pentwise by her hands, which covers her head, looks down, with painted eyes and brows showing above a bandaged mouth, at the fumes of a beautiful censer or chafing-dish placed on the carpet." (Source: http://www.jssgallery.org/Essay/Harp...y_James688.htm)
Does that help? (I'm not sure it helps me!) It sounds as if it's referring to the shape of the cloth made by holding it over her head but I'm not clear on how that fits your original sentence.
Also, see the definition of a "pent roof" here.
Student or Learner