Although we talk about fantasy, considering the evolutionary aspect I would state that some hominide species should have females with beards.
Uatu is probably right that there is a psychological barrier preventing us from imagining bearded woman. Fantasy artists (at least the well-known) generally tend to draw beautiful women rather than ugly (just look at Uatu's and Manikus' character pics
). Thus the (probably repulsive) bearded female dwarf is seldom depicted.