That's a difficult question to answer. I think the contexts are different for why people join militaries.
I taught at California State University in the U.S. before I moved back to Canada, and I remember the ROTC being on campus and having genuine difficult recruiting, and at some point we were kind of wondering why. It was because there were so many active conflicts in the world, and there were people who were not as interested in joining militaries, and that was at the same time as the U.S. lifted the “don't ask, don't tell” policy and allowed women in active combat.
Many people chose to see that as a form of post-sexist enlightenment, of post-homophobic, post-sexist enlightenment. The idea was that we were going to have everyone. I was a bit more cynical. I thought it was pure scarcity. They weren't getting enough people to sign up.
Therefore, I think that in different contexts, women are as likely or as unlikely to join militaries. I don't think that's something we can necessarily rally around and encourage women to join. If they're interested, they will join, and over time we will see change.