Thanks for the reply.
The bike originally came with an adjustable length stoker stem, but the minimum length is HUGE, nearly 200mm. All the adjustable stems I have found have a minimum length much longer than fixed length stems, which vary between 110 and 130mm. The Rock and Roll is officially a mountain bike tandem, and came with mountain bike handlebars, though the large majority of our riding will be on the road. We chose a "riser" bar for my wife, which gives us some flexibility to add height to the bar, even if we choose a short stem that attaches to her handlebar under my saddle. Plus, we will add bar ends to it to give more hand positions. Without a doubt, she will be more upright, with the bar height capable of being higher than her seat height. It's the length that I'm wondering about. With the current "cockpit" her length from seat to handlebars on the tandem would be a few inches shorter than the equivalent space on her road or mountain bike. Is this also typical on tandems, or should we try to get the same cockpit length she has on her single seater bikes?