So I recently posted this is another companion thread, but I don't think that the 6:3 gender ratio is that unlikely. It's not ideal, certainly, but it's not like we couldn't have somewhat similar ratios in other games.
If we look at a male mage Hawke, he's got 8 companions (including Sebastian) and it's a 5: 3 gender ratio.
And if we look at DA: O, we've got 9 companions with possibly only 3 females depending on how you count Shale. I tend to consider her a "her", but she seems to not really identify as a female (Isn't there a dialogue with her about her gender identity where she discusses this?), so it's a bit fuzzy. If you don't count her as female, then it's 4 males, 3 females, a genderless golem, and a dog (who's technically male).
I guess, I'm just saying that, while I would really like another female companion (also would love a lady dwarf or lady qunari), I just think it's becoming more and more likely that it's going to be just the three that we know about. I'm having a hard time believing that if there was a 4th lady companion, we wouldn't have caught sight of her somewhere by now. She's not in the concept art, gameplay footage, leaked survey, magazine articles, PAX annoucements, etc. Unless they are purposefully hiding her, that seems like a big coincidence (although I guess it could be possible). I think that the only gals that we have seen and haven't been able to figure out their role are Scribe Girl (who's almost certainly not going to be a companion given that she's never been shown in the field or with a weapon) and the blood mage apostate lady from those two concept art pieces about the templars. I'm thinking that she is probably just a random character for the pictures, though.