After you buy her a nice light field gun, her next complaint will be about the recoil.
Felt recoil is a factor of the weight that is being accelerated versus the weight available to absorb the energy (the velocity to which the weight is being pushed is also a consideration, but commercial shotshells are all in relatively the same velocity range, so we'll ignore that factor for now).
The weight being accelerated is the amount of shot. The weight available to mitigate is the weight of the gun. As soon as you reduce the weight of the gun, the felt recoil will increase.
Many hunters/shooters are under the misimpression that more shot in the shell equals better chances of bringing down the game. This is simply not the case. There's an optimum point beyond which shot patterns actually get worse as you add more pellets to the shell.
If you want to resolve the gun weight problem without creating a new issue in the process, be sure to pick up some 7/8 oz loads for that 20, if you go that route. Where there's a choice, choose those with the least propellant (lower "Dram Equivalent" number). Heavy loads and magnum loads are an advantage with waterfowl and tough species like pheasant or sharptail. For most everything else, they just beat you to death and offer REDUCED performance, not improved.