She is carrying what appears to be a submachine gun of some kind...so why does she carry what appears to be approximatelly 6 shotgun shells on the front of her vest? I only assume she is doing a not-so-commonly known tactic of carrying a small amount of somebody else's ammo to ease their load.
I know, I was just trying to 'make a funny' so-to-speak.
There is a real-life tactic, however, that could explain that. Sometimes somebody's load might be a bit on the heavy side so a second agent/operative/officer will carry some of their ammo or some other piece of equipment for them.