There are some logistical problems that need to be overcome. For example, current Army regulations state that females must have access to bathing facilities every three days. You really can't provide that if you're a front-line unit. Since you're the first in, you're living off what you can carry, and it ain't much.
Even if you're stationed in a forward operating base, any combat unit are operating out of patrol bases for a month at a time (for the uninitiated, it's a spot that's way out of the way of major routes of travel, major terrain features, and close to some sort of water sources usually, occupied for no more than 24 hours) because the enemy needs to be found and killed, or the population needs a sense of security way out in the boondocks.
Personally, if they can work out stuff like that, and if the female in question can pass the male version of a pt test (currently, the female max score is failing or barely passing the male minimum score, and the new pt test they're coming up with is supposedly unisex, but I doubt it'll turn out that way) then why not ?