In Morrowind and Oblivion Boethiah was most certainly portrayed as a man with a male voice and statue, but in Skyrim (s)he is portrayed as a woman with a feminine voice and shrine.

Wut?

Daedric Princes don't have a gender. They can take whatever form they please.

I do believe all Daedric Princes are genderless, though I might be wrong.

Daedric Princes are both male and female, and neither at the same time. It is simply up to how they choose to portray themselves at any given time.

And Boethiah is particularly noteworthy for liking to change.

Is Boethiah a man or woman? ... Yes.

Daedric Princes are whatever gender they want to be. Although I think Boethiah gravitates more towards masculinity than say, Vaermina.

Just imagine a female Sheogorath.

http://static02.mediaite.com/geekosystem/uploads/gallery/creepybiebergirl/cg1.jpg

A question a bit more appropriate for the Lore section, but Boethiah is neither and both.

Even Sheogorath is not male.

I can garuntee that even Nocturnal is not female.

Boethia is referred to as both a Male and Female, though Skyrim is the first time Boethia's aspect is female.

Of course, Daedra lords are beyond something so fundamentally mortal as a biological "six". I have a theory that all Daedra Lords actually look as Herma-Mora appears, but they choose to manifest and maintain different guises because of their particular delight in meddling with Mortal Affairs, whom would find a mass of tentacles and ether to be entirely unrelatable. Mora is one of the Daedra that isn't known for being particularly interested in the happenings in the Mundus, so he (it) doesn't really care.

I had to google that based off of the image name to find this:

http://www.youtube.com/watch?v=qyWczXey0IQ

Sheogorath is far more interesting.

One sixy dude, then.

Honestly, she's kind of cute and not at all creepy until you stare at it for a ridiculously long extended gaze.