Don't get her the .410, it will only frustrate her because she won't be hitting much. Assuming she's under about 5 and a half feet tall, I suggest you take a good look at the Mossberg Bantam pump gun in 20 gauge. The key to making a 20 gauge user friendly is to get light target loads. I use light target loads and taught both my kids to shoot with it, and my wife enjoys shooting it too. The reason for the Bantam, which is marketed as a youth gun, is that it fits smaller people. My full size shotgun is simply too big for my wife.
Another important thing in using the 20 gauge, or any other gauge, is that the new shooter must absolutely understand and apply the following: The gun must fit snugly into the shoulder, and the cheek must be snug on the stock. If either of those don't happen, then the user will perceive harsh recoil. JUst be patient and make sure she applies this lesson and understands why it's important. The first shot my son fired with the Bantam was a good one. He heeded the lesson. His second shot, he didn't heed the lesson and started crying and wanted to go home. I told him why he got hurt. Insisted that he take just two more shots, but with correct form, and he did alright. Next session he was comfortable with the gun.
Back to the Mossberg: It's one of the best deals int he shooting world. You don't get a chromed bore or fancy cosmetics, but you get a superb gun for the money. Tang safety, tapped for a Weaver scope mount if deer hunting is in the future (ours gets great accuracy with the 2 3/4" Rottweil slugs and poor accuracy with Federals). Nice fit for people of short stature.