I know a whole lot of female otaku that are gaijin. Most are fat and bitchy, but some are nice looking and kind. They kind of span across the entire spectrum.
There are a lot of japanese female otaku too, i chat with some over peercast sometimes.
There used to be a documentary on female otaku by some japanese tv program on youtube. I can't seem to find it now though....
I'll post if i find it.