My wife hasn't ridden a bike in a really long time, like 20+ years. I'd really like for us to ride tandem, but she feels unstable and unsure on a bike now.
I'm wondering if a low slung bent might be a solution to helping her overcome her fear. I'm thinking the position (laid back, heads up, no sore butt), and the ease of putting a foot down might boost her confidence. Test riding is definitely in the works, but I'm wondering if anyone here has had experiences similar to this that might be helpful.

Do you have any recumbent riding experience?

My wife and I have had a lot experience riding conventional tandems. Following an injury we decided to switch to a recumbent. The acclimation process has taken a lot longer than I expected. In our case I'd have to admit that it's my anxiety that's the biggest barrier. I'm having a hard time getting comfortable and confident on the recumbent. It's just a completely different thing.

If you haven't done it already my advice would be to get the feel of riding a simularly configured single recumbent first.

One of the cruiser-style conventional bikes with the crank forward design might be better for your purpose. It still allows the rider to put a foot down when needed but handles more like a regular bike.

My bride never rode much at all. She comes from the mentality that bikes are toys and a ride consists of once or twice around the block on a Sunday afternoon.

She is fully capable of riding both singles and tandems though she does not share my affinity to bikes. When she did ride she didn't have a lot of self confidence in her abilities.

Knowing my love of cycling, she has often agreed to go for a ride with me. Of course those rides were generally less than 10 -15 miles and at a nice comfortable 12-14mph pace.

Eventually uprights became too difficult for her to ride for various physical reasons and I purchased a used EZ Tandem. Now I had approx. 1000 miles of LWB recumbent experience already so I was able to readily acclimate myself to the tandem. Our test ride prior to purchase consisted of my taking the bike around the block once, solo. When I got back, she just hopped into the stoker's seat and away we went. She hasn't climbed up onto an upright bike since.

We still don't ride together very often, but when we do she's comfortable, relaxed and confident.

A year later I bought her a Sun X-1 which she learned how to ride after a fashion. I believe she still prefers the tandem though.

Your own results may be different.

When we first met, my wife had already done some riding, including some supported touring. When I got my first commercial 'bent (I had built them previously) I let her coast around a parking lot on it. She immediately said "get me one". 20 years later, she's still riding recumbents, and we've been married 18 years.

She's tried riding uprights occasionally since then, but never with much success. We've also tried riding tandems, but she wants to be in control of her own bike. Whatever. It works for us.

Depends upon what is the source of her fear. If it is simply falling off, then a two wheeled recumbent is not going to be much better than an upright. I've had a few people who regularly ride upright bikes give up on a test ride on either my LWB Linear (which is very easy to get accustomed to) or to my Haluzak Horizon SWB which is a bit more difficult to ride.

Let her try out a recumbent trike. There is no learning curve and even people with severe balance problems can ride them with a secure feeling. Just be warned that if you think regular recumbents are expensive, the decent trikes are even more expensive. I'd suggest looking for a used one since that makes them much more reasonable in price. If you really want to get outrageous in price go look for a tandem trike!

Bents are notably harder to ride for the first 50-100 miles even for the experienced
DF rider. Balance and steering are more of a challenge so this must be taken in
to account. I will never forget loaning my Rotator to a lady for a ride down the street
and she was unable to stay up even on a gentle down hill and with me trotting along
holding the seat. Same lady hopped on a pogostick a few years earlier and within
a minute was making the thing eat out of her hand, unbelievable balance on the pogo,
no go on the bike.

I've noticed that "experienced" DF riders often have a lot of difficulty adapting to recumbents, but relatively inexperienced riders pick it up quickly. I think this is because experienced riders are used to pulling on the bars, which doesn't really work on a recumbent. IMHO, of course.

Recumbent tandem trike?

If she's worried about falling, a trike would be a natural. No need for a tandem.

I've looked at trikes as well. For some reason I have it stuck in my head that trikes are slow and harder to move. Her "fear" is instability and lack of confidence on a bike. She's afraid of crashing and of traffic. The nearest bent dealer is an hour away, but we'll try to make the trip and do a test ride. They have 2 wheel and tadpole singles and tandems in stock.

I have a Slipstream and I'm a seasoned DF rider. I can say first-hand it takes time getting used to the "feeling" of a recumbent. The physics are the same but the configuration makes everything you've learned to expect come from new directions. For example, gravity is felt in front and below you on a DF but on a recumbent it's now behind and below you. The long wheelbase makes turning a new experience and when you stop, you are not poised to take a standing posture. On the Slipstream you bend your legs at the knee and put your feet on the ground but most of the weight is directly below your butt so a bit of extra effort from your legs is needed until you get used to the new sense of balance (stopped). Turning takes more of a conscious effort since you're sitting in a chair instead of balancing on a saddle and can simply lean to turn. The chair makes you forget to lean into turns it seems. At least that's my experience.

But in spite of all this, the recumbent is a pure joy to ride.

I've tried a trike (Catrike Expedition) and the first thing I noticed was no leaning at all. This feels weird in turns and you have centrifugal force to deal with if you're turning a tight corner at speed. The other thing I noticed is a rougher ride with three wheels picking up the road bumps instead of two. On the Slipstream you literally feel like you're riding a hammock on wheels. I suppose they all have their pros and cons but recumbents in general are a lot of fun.

What's "DF"?

Diamond Frame....as in an upright bike.

Just got the wife a Sun EZ 1. It took her one time around the block and she is ready to go.She was riding a Revive DX so was half way there.
Now it is the only bike she will ride.

I struggled with trying to (gently!) coax my wife into cycling as well. She was always agreeable with the idea, but it never really worked out. A recumbent trike totally changed things, she now commutes to work on it, and is becoming increasingly confident and adventurous cycling.

Just be careful. Take it easy. Use due caution.. Like to say a bent is totally safe, but a friend crashed on a bent. Suffered multiple broken ribs.. He was downhilling super fast.. He was going like 40 mph plus. Still, nothing will keep me off the bike. Neither bruised rashes nor nagging wives..