Any model with bluetooth can use a separate keyboard. You'd simply need to find one that would be suitable for her.
There are keyboards that are rechargeable, and there are keyboards (larger) that use AA or AAA batteries.
There are some keyboards with Android key layouts. Those are usually OK, but some of the keys are odd because they set them up to use the keyboard as a replacement for using the touchscreen for navigating in addition to typing. There are a lot of ordinary layout bluetooth keyboards that still work fine. With those you're still responsible for opening apps or navigating menus via touch. All they'll do is type letetrs and numbers on a phone/tablet/phablet.
There are even cases with bluetooth keyboards already attached (see below). Those usually follow the Android key layout, but not all do. The trick there is to find a case that's the right size for the phone and allows access to buttons (power and volume) plus access to the charging port. In most cases a universal case will work for that, but they don't usually come with keyboards. I set one up myself 6 years ago for a tablet I had that I couldn't find a case for. I bought a universal case, bought a small, thin bluetooth keyboard and used small pieces of velcro on each corner to hold it to the case. It all folded closed just fine without any pressure on anything. I still have that case, keyboard and tablet.
One problem is the phablet. Tablets are generally 7" or larger, while phablets are nearly always smaller than 7". Finding a case that can accommodate a similar-sized keyboard may not be an option. Even finding a similar-sized keyboard may be out of the question.
If she has the space (large purse, for example) she could carry them separately and the size of the keyboard wouldn't be as big a deal. Since she wouldn't need a keyboard as much, that would probably be the best option anyway. Then she could take the keyboard out and turn it on when she needed to type things. Or simply leave the keyboard at home and only use it there.
I can't recommend phones or phablets, though. For one thing, I don't use Verizon. I aways use a phone for a phone and a tablet for everything else. But I can say any phone should work fine with any keyboard (except the iPhone is really trashy and picky about what it will connect with). Bluetooth keyboards can be had for as little as $10 and as high as a hundred or more. I wouldn't go too cheap since those often don't last long, but higher-end are totally unnecessary unless it's used a lot for special things. I've had good luck in the $20-40 range.
I mentioned the iPhone. I'll add here that I really don't like Samsung either. I've had several of their products (phones, TVs, a tablet, a washer) that were not only less than optimal, but downright flaky. My son has a Samsung phone he got to replace another phone. I'd warned him about Samsung (plus he had one of the earlier phones that were trash), but he got one anyway. The day he got it, the screen turned red on him. There was an update. After that, the screen was fine for about a month when it turned red again. He could reboot and it would be fine for a few days to a couple of weeks, then turn read one more. That went on for 2 months, and now rebooting doesn't fix it. It's red-red. more like reddish. Like a screen set up with blue filtering to lower light output at night. His is like that all of the time. Their tool to change coloring does nothing. That phone is in addition to 4 TVs (2 went flaky), 2 older phones (both became unusable after a little over a year) a washer that was replaced by another washer that did exactly the same thing as the first one that was broke, a tablet that was not optimal when I first got it and went downhill from there and so forth. Don't think those were the oddball cheaps products either. They were all top-of-the-line or one generation old top models when we used them and they were trash. Especially the washer.
Did I mention I don't like Samsung? They're a Korean company. When I was stationed there, Koreans didn't like Samsung either. I thought maybe they'd gotten better in the 20-25 intervening years after I left there and started buying some of their stuff. I should've followed their lead and bought something else. I do now. It took me a few lemons to realize that truth.
Back to the keyboard, remember: turn the keyboard off when not in use. That reduces battery drain, but it also prevents accidentally typing and sending things out you didn't really want sent if it's being carried around and bumping into stuff. Also make sure it's bluetooth and not one of those that plugs into the charging port to use. Trust me, nobody wants the headaches those kind cause!