Unclear, but a still considered a serious problem. With the parameters of the statement provided, it is difficult to definitively confirm or refute it. In order to do so we would would need to know the time frames involved (e.g. one year versus the entire campaign) along with what "attacked by the enemy" means. The latter could be resolved through the use of proxies such as combat awards (e.g. Combat Action Badge (CAB), Combat Action Ribbon, etc.), but the award of the CAB for indirect fire (i.e. mortar attacks) means that someone can be attacked by the enemy without directly engaging them in combat. As such, the question itself will likely remain unresolved without more information.
That being said, sexual assault of women deployed to combat zones is considered a serious problem:
Deployed women exposed to combat-like experiences reported a 20
percent incidence rate of sexual harassment and a 4 percent rate of
sexual assault during the three-year follow-up period after the
Rates of sexual harassment and assault varied by branch of service.
For example, the rate of sexual harassment for women in the Air Force
and Navy was the lowest at 5.8 percent. That rate in the Army was 10.3
percent, with the Marines having the highest at 13.3 percent.
Female Marines also reported the highest rate of sexual assault at 6.6
percent, compared to 1.6 percent reported by Air Force women.
And then, of course, there’s the issue that’s received so much
attention in the press of late: the prevalence of rape and sexual
abuse in the military. While none of the women I spoke with for this
story had suffered from military sexual trauma (MST), the armed
services’ catch-all term, an estimated 20 percent of all women who use
VA health care have been sexually assaulted, abused, or raped during
their time in the U.S. military. Civil rights groups that get their
stats from independent researchers put the number even higher, at
around 30 percent.
Numbers reported by the Department of Defense show a sickening
pattern. In 2006, 2,947 sexual assaults were reported -- 73% more than
in 2004. The DOD's newest report, released this month, indicates that
2,688 reports were made in 2007, but a recent shift from calendar-year
reporting to fiscal-year reporting makes comparisons with data from
previous years much more difficult.
The figures reported in the news can be traced back to work done in part by the Department of Defense Sexual Assault Prevention and Response Office who have been producing annual reports on military sexual assault since calendar year 2004.
The quote itself is also remarkably similar to a statement made by Representative Jane Harman:
"A woman in the military is more likely to be raped by a fellow
soldier than killed by enemy fire in Iraq,"
This similarity is noteworthy, but killed by enemy fire is a significantly different bar to meet compared to "attacked by the enemy." If this is the origin of the statement in the question, then it is much easier to to check. As of December 22, 2014 there were 110 female deaths as part of Operation Iraqi Freedom, while 143 reports of sexual abuse were made in Iraq for 2008 alone.