What do you mean by foot soldier? Also don't call a Marine a soldier as they find that offensive. :D If you are talking about going into combat then the answer is no. Women are banned in the US military from going to the front lines of the battle and have open combat.
Women are trained to fight and defend themselves and might find themselves in a firefight but that would be accidental like in an ambush situation.
No. Not yet at least. But they can join