Get her one
It will certainly be beneficial for the both of you, just don’t get a tandem.
Brian
The Mystic is a beautiful boat
Althouh my wife is not tall, she is a little bit chunky (I hope she doesn’t check these boards). She found the Mystic very tight and the Montauk a better fit.
One of the Loons?
First off, I’ll admit that I don’t have a lot of experience with a variety of kayaks, including yours.
The first kayak I ever paddled was a Loon 111 [old town canoe]which was a lot of fun but a bit tippy for me.
Next, I rented a Loon 138. It was MUCH more stable, for my size and weight, and I just loved it.
Loons come in a variety of sizes. Maybe one will suit your wife.
Try before you buy is good advice.
Good Luck!
I have 4 very different kayaks
One being a Dagger Blackwater 10.5-I LOVE that yak and all of the other 3 yaks! Being that she’s a beginner I would get the same one for a starter yak and if she wants to move into another type then go for it!
Caution!
Don’t go any shorter than a 12 footer or you’ll regret it in a couple of months.
Dagger Charleston 14
My wife is 5’ 4" and paddles a Dagger Charleston 14. Very stable and easy to paddle … but it is not a barge. It has a skeg. Highly reccomend if you can find one. Impala Bob
Ummmmm…
Ummmm… nobody has mentioned this, but why not let her try yours! If she likes it, you need look no further. Also, I’d highly recommend you find a dealer that’s having a demo day and both of you try out as many yaks as you can. Keep your eyes open for used ones too.
My girlfriend
Is 5’2" and 112lbs. she started paddling in Dagger Callisto. Callisto is a very stable good entry level boat made for small paddlers. There are still some out there for reasonable price. She is now enjoying a Necky Elaho Sport that she loves. It is a bit more tippy, but much more responsive and playful. Her daughter at 4’11" and 135lbs. owns and loves her Old Town Castine. Always good to demo, demo, demo. Good luck and may your wife enjoy paddling as much as my kayaking obsessed girlfriend.
Reverse roles leads to clarity
I really second the step back allow her to take initiative and responsibility for this rather than you make these decisions for her regardless of how nice your intentions. Reverse roles and think how it feels if she was to think she knows what is best for you. Our culture has lots of hidden sexist attitudes we are seldom aware of that operate here.
Regardles if people demo or get day of instruction same process having them learn about dynamic seat and body fit, sitting upright, being connected to boat, learning to forward paddle and direct themselves, all the while gaining comfort and more relaxation with the boat.
Only then do people make wise and accurate choices regarding their boats and with a dealer that has their interest at heart. If you get yourself into this, it prevents her from doing the thinking, feeling, and practicing to make the decision.
Best gift is to step back, something guys have little training to do.
My opinion only of course.
I’m 5’4",
decidedly chunky (146 last time I braved a scale) and the Impex Currituck fits me fine. The Montauk might be good, too.
Blackwater
I’m a tall woman…but I find the Blackwater 11.5 to be very stable. My husband and I tried both the 10.5 and 11.5, but found that the 10.5 was quite “shakey” when leaned, while the 11.5 maintained excellent secondary stability.
Started Stable…
I’m 5’2" and started with a Carolina 14.5. Very stable but it swallows me. Consequently, I have a hard time paddling because the water is so far away! I’m keeping it for paddling guests, but I’ve ordered a narrower, sleeker boat. So definately demo if you can!!
Think about a folding kayak.
Generally stable. Great for travel.
Pungo
I bought a 12’ Pungo for Kathy last year, and she loves it. I am very impressed with it myself.
I had the typical rec boat bias that most ocean boaters have, but she saw it at the Santa Cruz Surf Festival and she liked the seat.
I wanted her to have something that suited her needs, not mine. Since she is adamant she will not do whitewater, or open ocean, I figured why not?
I would strongly recommend against it for whitewater or ocean, but on flatwater is is great. Inch for inch the Pingo is an amazing little boat.
Hurry
Before she changes her mind.
Brian
Pungo 12 / Blackwater 10.5
We have both of these boats that we bought as our 1st boats several years ago and have kept them for river use as we don’t mind when they get banged on the rocks.They are easy to handle on rivers and are fun. The Pungo is extremely stable and holds lots of gear easily - my husband uses it as it feels like a bathtub to me.I love my little Blackwater as it fits me, has a skeg which you can use if you want and is easy for me to lift on top of the car. Both of these boats are great for company to use as they both feel very stable. My other boat, a Catalina made by Prijon is actually much more stable considering secondary stability but newbies always go over in it.But if it were me, I would want to choose my own boat 
A Current Designs Slipstream
Thank you for all of your help last year when I posed this question, being over 50, 5’2" and about 120 pounds, you suggested this boat. After going to as many demos I could in a few cities, I found this boat, 22" wide, 16’ long, that I can use to keep up with the guys. I don’t feel pregnant because it has a nice low foredeck, and the secondary stability is fantastic. So try the Slipstream, I am sure she’d like it. Enjoy!
Great Advice Everyone!
First, I agree with everyone that said take a class. My husband and I took a “coastal kayaking” class together. Then, we went out and each of us demo’d kayaks - sometimes switching back and forth with the yaks. Ultimately, we ended up with totally different ones. As others have said before me, I preferred the “tippier” kayak and he preferred the more cumbersome one. We switched last year for a run and both of us could not wait to get back into our “own”. It was definitely a decision based on feel and proper fitness of the kayaks for both of us. It is a wonderful sport to engage in as a couple. We both love the peace and tranquility. Plus, we know enough places now to pack picnic lunches along the way! Have fun but, don’t forget to have her demo her own kayak.