What men are you hanging out with? Pretty embarrassing!Most men can't properly handle the recoil of a shotgun so I doubt very many women can either.
At close range (such as a house) a shotgun blast will land like a bullet, very tight pattern.
Teach your mother-in-law how to shoot with a .22 pistol and go from there. Basically, the biggest handgun that she can shoot and handle well in the biggest caliber she can shoot well is the answer.
If that's a .22 LR then so be it.
Also, it's a good idea to put a set of ear pro muffs that allow normal sounds while blocking out gun shots by the weapon and train her to put those on when she thinks the fun is about to start.
Having lost part of my hearing at age 15 because my father thought earmuffs were stupid has really sucked these 50 years. It'll be really loud shooting inside her house.
Also train her to never fire through doors and never go outside to address sounds or intruders.
Don't forget teaching her good tactics and why a flashlight with strobe effect is priceless.