An off the shelf Colt 6920 with an Aimpoint H-1 Micro and a backup iron sight is going to weigh around 7.5 lbs. It's about as stupid proof as you can get.
Alternatively a Bravo Company Model 1 or similar (near identical to a Colt) would do the same.
In her case, avoid rail systems, keep a basic (standard or MagPul MOE) stock on there, and a decent sling.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."