What’s the best shotgun for a petite lady?
Mossberg 500 turkey
If you don’t want the 12 gauge you can go with the same version in 20ga.
I'm big, I'm experienced, and I have low recoil loads in every shotgun in my home (except the last round is a magnum so even if I lose count, I'll know it's the last one). Low recoil is much easier to handle and much more comfortable to shoot, especially if you don't weigh much.
Best shotgun has a lot of answers, all of them right. I personally love the Remington 870 Express Tactical/Home-Defense Shotgun. I hate the Remington 887, which is advertised as having the same design and a better anti-rust coating (not true on the action) - mine has jammed or failed to fire many times, as has the 887 for other owners, and the 870 has never done that.
People here and on the range also like Mossbergs 590 A1, and the Saiga SGL, along with several others, and I'll agree that they are good too. My personal preference is for the Remington 870 because it's simple and completely reliable, but I'd encourage you to shoot several models before choosing. There are already a lot of "best shotgun" threads on FR with excellent suggestions on which one to choose and why.