This is news to me. Would you elaborate? I've got a daughter hard set on a military future.
I could answer this in two words: Jessica Lynch. How ever I'll steer you in other directions.
I'd look at the Army Times story covering the dismal performance of females in the Army. The average white enlisted female does not make it through the first four years of their enlistment. Typically, they are separated for pregnancy, other physical problems (many the result of too rigorous training) and/or failure to perform. Read the article, and keep in mind the Army Times is a liberal paper.
Robert H. Knight of the Concerned Women of America has written extensively about these problems.
I would also steer you toward the current figures regarding preganancies, abortions, evacuations from the field, failure to conform to military life, etc. that indicate extraordinary problems integrating female soldiers into the force. The problem is that the Army (and other services) don't make any of these public. You can guess why. What I've written applies to the Army, Marine Corps, Coast Guard and Navy. The Air Force, by virtue of their mission, is a different animal. I'll let somebody more familiar with the Air Force comment on that service.