I’m not looking for a bunch of extra suggestions, just a straightforward answer. Thanks.
A lot of people think shotguns won’t go through walls, but that’s not true. If you’re small (like 85 lbs), a rifle in a smaller caliber like .223 or something in 9mm is probably a better option. Most defensive ammo can go through walls if you miss.
The key is to pick something lightweight with low recoil so you have better accuracy. Shotguns don’t spread much in a house—only a couple of inches—so you still need to aim carefully. Plus, the recoil and weight might be harder for you to handle, which makes missing more likely.
@Bryant
A 9mm carbine could be a good option. It’s easy to handle for someone smaller, and there are plenty of good ones available now.
A .410 with #4 buckshot has less recoil than a 12-gauge. Paul Harrell on YouTube has shown that #4 buckshot can be effective without as much risk of over-penetration. I’ve got a Mossberg Shockwave in .410, and it’s a fun gun to use. Just be aware that the pistol grip on the Shockwave might not work for everyone depending on your setup and abilities.
Take a look at youth shotguns. A 20-gauge or .410 wouldn’t beat up your shoulder as much. I’ve always been a fan of Mossberg—affordable and reliable.
Honestly, I’d recommend the same thing to someone bigger. A Beretta 1301 or A300 could work. They’re semi-auto, which means less felt recoil, and you can find shorter barrel models to make them easier to use.
Just know that shotguns aren’t super beginner-friendly. The controls can be tricky compared to a rifle like an AR.
@Callen
This is solid advice. A lot of the other suggestions here aren’t great.
Any home defense gun can potentially harm neighbors. A shotgun with 00 buckshot has a lot of over-penetration potential. If you’re not experienced with shotguns, a pump-action is a bad idea for home defense—it’s slow to chamber rounds, messes up your aim during reloads, requires more strength, and can easily jam if you don’t rack it properly.
You might be better off with an AR15 or a pistol-caliber carbine. They’re easier to use and handle.
My wife is 4’11” and handles my Sig MPX-K perfectly. It’s a 9mm and barely has any recoil. It’s a great choice if you’re looking for something smaller and effective.
Sorry if people are giving you a hard time. There are shotguns made for smaller frames—junior models—that shoot just like the regular ones. It’s safer and easier to handle if the gun fits you well. Don’t be afraid to ask for help at the store; they’re there to assist and make a sale.
@Dragonsecure1
My only issue with junior shotguns is that they usually don’t hold much ammo, and you can’t upgrade the capacity.
A double-barrel 8-gauge, obviously! But if you see a 6-gauge, grab it… kidding! 
Shotguns can work for defense, but shorter “tactical” models are better in tight spaces like hallways. Some folks recommend 20-gauge for less recoil, but I’d stick to a 12-gauge with reduced recoil ammo. It’s easier to find and more effective.
Whatever you pick, make sure to take a class that focuses on defensive shooting. It’s worth it.
After all these unhelpful answers… are you still looking for advice?
For home defense, go with a semi-auto shotgun. It’ll absorb some of the recoil and be easier to use for follow-up shots. If it’s just for fun like trap shooting, you could try a 20-gauge, but I’d stick to 12-gauge for defense. Look into youth models—they’re smaller and easier to handle.
@Masitsa
Nope. I’m done with this forum. Same nonsense I hear at gun stores. 
Gus said:
@Masitsa
Nope. I’m done with this forum. Same nonsense I hear at gun stores.
What happened? Why so frustrated?
For a smaller shooter, a 12-gauge tactical shotgun with a short barrel and semi-auto action is a solid pick. Add a flashlight to the rails for home defense. But honestly, an AR15 might be easier to use because it has less recoil and is more customizable.
You should check out the Black Aces semi-auto shotgun. It’s compact, affordable, and works well with good-quality ammo. If you’re into magazine-fed shotguns, you can even get a drum mag for it. It’s fun and reliable as long as you maintain it properly.
Mossberg 590S all the way.
I use an AR-15 chambered in .22 for home defense. With a 25-round mag, it’s effective but less likely to over-penetrate walls. It’s also easy to patch drywall if needed. Just my two cents.