It's not a "natural instinct." It's entirely a cultural thing. It just appears inborn because of the way gender socialization works. Just like every other aspect of gender.
Regardless- it is there and would be an issue
Aside from that, women are less physically prepared for combat. There is a reason PFTs for women have lower standards...females are simply unable to push the limits of physical strength and stamina of men. Hell any woman serving right now could do far better then most male civilians in a physial contest... but women are unable to reach the required physical level for combat