If she is on the smaller side the 3901 redced length model is the most adjustable right off the shelf foe less than 1k new. Try mike @ silver dollor firearms he had a great price on them. They can easily be made into a full size later. Mike had some stocks to I think.
I too am a lefty and when I started shooting recoil bothered me. I eventually was able to convince my dad to let me use his 11-87 field gun instead of the pump that I was using even though it ejected shells to the right. I loved it and its soft recoil and started looking for a left hand version for myself. I eventually found a used 1100 which I bought and shot for 2-3 years. Then the hunting bug bit and I decided to move into an 11-87 of my own. My dad encouraged me to keep the 1100 for a year or two until I was sure I like the 11-87. I loved the 11-87 also but I just couldn't get it to cycle properly for doubles (not a problem with the 1100). I moved into a browning XT and shoot it well but the left hand 1100 still hasn't found a good home. If you are interested I can send you pictures. I also have an adjustable stock that could go with it. When I got mine to fit recoil was never an issue and I don't think I could recommend a better gun. Let me know if you are interested.
an issue that needs to be addressed with the remingtons is the placement of the safety. It needs to be plugged or customized to be reversed as it interferes with the trigger finger of a left hander. Beretta's are not in the way and can be easily reversed if required...
I am left handed, been shooting for 40 years. If you decide to purchase her a semi automatic, only consider a left hand model. To my knowledge in trap version the only gun available is the Remington 1100 trap. The reason I suggest a left hand version is once in awhile if you are left handed and are shooting a right hand semi auto you will get blow back to the face and eyes and it feels like someone slapping your face. It happens when you least expect it, it doesn't happen that often, but when it does happen it is a shock to you, and believe me after it happens you will have trouble not lifting your face from the stock, fearing that it will happen again. I love Remington 870's, but they kick way to much for most female shooters. The only other gun that I would consider if it was my daughter would be a BT99 micro, or an old style BT 99 made prior to 1976 with a 32 inch barrel. There is one being offered on TS.COM new in the box as of the other day. Hopes this helps.
I would look at getting an older beretta 391 urika parallel target with an RL stock and 28" or 30" barrel. She can shoot all disciplines and upgrade to an over under when she decides that it's time.
I've been watching this site for a lefty 1100 for a year and there have been 2 sold here in the past year. The last one was assembled from parts, but the previous one was the newer discontinued model. The bottom line is that she might be off to college before you find a true left handed autoloader unless you go to one of the other forums?
I mentioned thia on another thread for someone looking for gun for wife: P. O. David of Baton Rouge has a BT-99 Plus that he bought for his granddaughter but she decided she didn't like shooting. Almost a mint gun with factory recoil device and other factory goodies - notably adjustable comb and adjustable rib. The barrel is a 30-incher. He wants $1,250. Call him if you wish: 225 928-9738. Gun has a short stock, by the way.