Hey there,I initially found my 12bore a bit heavy, but that was probably because I'd never shot before. Now I don't find any problem with it most of the time. Occassionally my arms get a little tired when waiting for what seems like ages for some of the overhead targets at West Kent to come across, but not often. I use 28g cartridges and don't have any problems with bruising as long as I've mounted the gun properly.
Definitely make sure the stock is shortened if she's not tall. Mine's down to 13 and 1/2 inches and is comfortable. Maybe instead of getting the to chamfered off maybe look at going straight for a Jones adjuster or the adjustable Isis pad. I'm planning on getting one put on my gun, as I think for me its not just a matter of reducing the toe but also altering the angle of the stock to keep the gun straight.
Must admit I'm tempted to get a 20bore, but that not because I've got any regrets about the 12bore, I'm just hooked and fancy owning a second gun.
Regarding what is in bold. A Jones or Isis adjustable pad, does not change your pitch angle. It allows you to have the butt pad in the right place and move the gun around. Pitch requires taking a thin wedge, from the back of the gun, so that the angle of the pad, conforms more to the angle of your body at the contact point.
That said, the awesome ISIS Green Pad does come with a chamfered toe.