I've worked on projects where half the staff were female software developers. (4 out of 8). I don't speak for any women, and am only expressing my observations. What seemed to attract the female engineers I worked with to the company where:
1) Professionalism - It was not a frat house culture. People dressed and behaved professionally. I've worked in places where the developers were allowed to behave like we were still in college.
2) A strong work-life balance approach. Many of the women I worked with had children or were married and thinking about having children. 12 hour days, six day a week jobs were not what they wanted. This did not mean 39 hours a week, but 8 hours on the job and then maybe 2 or 3 after they put their kids to bed.
3) Strong support. If someone got into a jam the team rallied to help them out. It meant risk taking was not penalized. You could be less than 100% confident you knew how to get it done because someone was always there to back you up.
4) Good communications. Lots of face to face communication, feedback, discussion, etc. It meant that we talked things through before we ran off and write 10klocs of code. We explained our decisions and communicated them to the broader team.
I don't think that these attributes are specific to women, but I think the women I worked with responded well to an environment with these attributes. A lot of times we like to work in a kind of frat house/cowboy culture. If you're a real developer you'll work 12 hour days, slouched down into your hoodie, expect people to sink or swim, and tell people if they have questions to stop being such a bitch and 'read the code.' I think that turns some people off.
While these are certainly not the only reasons women don't get into computer science or engineering at the same rates as men, I think if you do want to hire qualified female engineers you need to 1) not lower the bar because no one wants to be seen as a quota hire, and 2) understand that the environment you create can determine who you attract.