Australia is attempting to allow females to serve in all roles in the military. I wonder if a female soldier would accept testosterone injections during war time if that meant making her more aggressive and stronger?
I agree with Kayla, you could ask the same thing about pumping men full of drugs too.
Also, being aggressive and strong doesn't really make you a useful soldier. Being level-headed and having good aim seems more likely to help. Personally I'd rather be protected by five cool-headed snipers than five roid-raging meatheads.