Bob, Sell The Gun!
Seriously if you don't think $200 is worth turning her into a shooter you sure as heck aren't going to like spending the big bucks for ammo to shoot 2.5 shells. Setting up to reload 2.5 shells and developing the loads to shoot are going to cost you some hard earned cash. So my opinion (worth every cent your paying for it) is to either sell the A5 as is or spend the bucks to modify it, including opening the choke to either IC or a lite-Mod, to allow you to shoot standard modern 16 ga ammo. You will be able to afford to practice with it, have the flexibility to buy ammo by the box for different shot sizes or different game, buy ammo on hunting trips, and be able to take advantage of sales on 16 ga ammo. You will end up with a true back - up gun for about everything but geese.
Scott