Up close, it probably doesn’t matter what shot you use. Still just in case, double ought buck shot, tho again any size buck would be fine.
I have an 18 inch barrel Winchester Defender next to my bed, loaded with 7 rounds of 00 buck. Despite the fact that I probably could not do better, I really would like an Italian Lupara.
They can be made very short overall as the action is short. Only two shots before reloading but that would probably be enough.
If mama might be using it stick with 2 3/4. The 3” might be a bit too much recoil for a follow-up shot.
If there is only one target. And you dont count the first shot as a throwaway.