So, C&C is not meant to be a realistic war game; not by any stretch of the imagination at this point. This isn't like making a historical, realistic Civil War game that the audience wants to play for authenticity and then making half of the soldiers female. C&C is not an authentic, realistic game and hasn't really been described as anything such since C&C95.
If you want to think of it in terms of the "realism" within the fictional world (i.e. what would somebody in this world realistically do) you would see quite a few women in combat service. The Tiberium Wars are a desperate, worldwide struggle where they need all the help they can get. I believe Tiberian Sun had multiple cutscenes where there were women in combat roles. Some of the pilots in C&C95 were female. Red Alert even had Tanya. There have been plenty of units with female voices throughout the series, and I really don't see this as an issue.
