I have similar problems. I have a lonely brahma rooster and saw brahma hen for sale at my local feed store. Took her home. To my surprise she started fighting and obviously dominating the rooster. I started to wonder is she was actually a she at all. The tail feathers tell me she is a hen yet she is one tough chicken picking fights with both o my roosters.
I would post pictures but I don't think I can post pictures with an iPhone . http://img.photobucket.com/albums/v517/Warrin/photo-1.jpg
Hope the link works that is the hen
100% hen. Either a hatchery quality dark Brahma or Light/Dark Brahma cross.