Not only do you get more cover this way, not all the enemies will follow you down, so you won't have to fight as many of them at once.

I found the Laser Chain Gun to be very helpful here, so try to save up some ammo for it if you can.

Once you get rid of the other soldier's, Petrova is cannon fodder for the Volt Auto Rifle. Keep on zapping her, she'll remained stunned and unable to return fire.

Hope that helps, at least a little