I wouldn't assume DD is necessarily 100% straight (though she might be for all I know). It's interesting that her very first novel was about a world in which supposedly there are no labels (no straight, gay, bi, etc.), and the sex is pretty free-for-all. But because marriage in that world is tied to childbearing/begetting (NOT to sexual fidelity), it's inherently between men and women, which, in this era of demagogues shouting about Adam'n'Eve-not-Adam'n'-Steve, grates on me. http://www.tor.com/blogs/2011/10/door-into-fire