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.
I use 2 3/4 for defense mainly because it allows a couple more rounds. Different brands of shells vary a bit in overall length. Enough that I have noticed my shotgun will take 7 of most brands but some it will only take 6.
With 3 inch it will only hold 5 in the mag. The only advantage of the 3 or 2 1/2 inch shells is pattern density. At 6 feet the advantage is moot.