Keep it civil.
A second-hand (pre-Cerberus/Freedom Group) Remington 1100 or 11-87 in twenty-gauge. I am partial to the “special field” version with the straight grip.
Any adjustable LOP would be aftermarket, or you can have her measured and get the factory stock altered by a competent gunsmith. Note that I wrote “gunsmith,” not “AR assembler” - the two are conflated far too often these days.
Thank you
Beretta 1301 or A300 can be adjusted by removing the butt plate and adding/removing included spacers using a screwdriver. If you install an adapter to use the Magpul shotgun stock it's even easier. Will look and feel like a ye-olde shotgun but be extremely light. Be careful though as full power loads will hurt.
Thanks
You could also consider a 20 gauge shotgun. They tend to be much smaller and certainly have less recoil.
Yes I am open to those suggestions as well.
In several places it's illegal to have a semi-auto shotgun with both a pistol grip and a collapsible stock. It's also illegal to have a shotgun under 26 inches in length or a shotgun barrel under 18 inches.
The Benelli Ultralight at 6.1 lbs is probably your best option. Here's an article with a few more options.
https://www.fieldandstream.com/guns/lightweight-12-gauge-shotguns/
Is semi-auto a hard requirement? Asking because I have long preferred break action at the range, and most trap/skeet shooters I've seen prefer pump or break actions.
If you're open to break action, something like the Stoeger Condor Compact in 20-gauge could be a good fit for a smaller adult:
https://stoegerindustries.com/shotguns/condor-compact-shotguns?eid=253
No but it is preferred to reduce recoil. As much as I love a pretty browning o/u they tend to kick harder.
Have you seen the reduced recoil shells like the Winchester AA and RST? That may help with the manual actions if they also fit well.
Does the stock length of pull need to convert back and forth? Is she small enough for a youth model?