I do believe that women in combat stand a greater risk at being abused than man, but that does not mean they shouldn't be allowed to enter war. They are aware of the risks involved and have a right to fight if they choose. It is important to give peolpe freedom, and make them aware of the harm that could result from it though.
Women are at a greater risk of being abused as prisoners of war because wide spread use of women in combat is still a fairly new phenomena in most countries. Historically, women have not been involved in combat except to tend to the wounded, or as slaves, or plunder taken by the victors in combat. Due to historical attitudes and the still sky high incidences of rape against women both in civilian and military populations, women are susceptible to a much higher risk of sexual abuse at the hands of their captors in war.