Well there certainly is a lot to think about here and thanks for all the suggestions. When I posted i did originally think of asking for the post to be removed on the basis that it was unsupportive and tactless.
Anyway, in response to what has been suggested:
The tandem came supplied with the Shimano single sided pedals and we did not like them. I because I use double sided and had a spare pair. Stoker, because she wears trainers and the weight of the pedal meant that it was SDP side up, which was painful on the sole of the foot, so they were replaced with an ordinary open set.
With the strapless clips that I bought; she could put one foot in whilst stationary, but the other whilst moving was too difficult. Possibly because there are other things to do/think of whilst moving.
Yes there is a grassed area nearby with a combined path/cycleway on it. May retreat there to start again.
Considering the wisdom of introducing change on her own bike first. There has been complaints of 'not having any control' on the tandem.
Having an SDP on the right and an ordinary on the left, which is the kicking-off foot. Brilliant idea!
Crank length. Yes this has occurred to me. MrsD2B is the shorter of the two of us. However a change here means replacing two cranks/chainwheels on both sides and I am reluctant to throw lots of cash at this time, especially when there are other issues to settle first.
Keeping both feet on the pedals is
not an option. Yes it is #3 Gaz. Written material presumes stoker is the lighter. Nuff said.
Bungee. Yes, worth a try
Tandem experience day. Yes this was suggested and did not get support on the basis that we can already do the basic mechanical stuff. I think that the underlying problem is that my stoker is a nervous rider, reluctant to take on new ideas. Her pilot, on the other hand, is an irritable, impatient, competent cyclist who finds it difficult to shrink his horizons and who makes an awful teacher. I think it's more a question of difference in perception, rather than mechanical dexterity.
Other problems yet to overcome:
Fear of speed.
Vocalizing terror when a car passes.
The concept that we are in the cars way and that we must defer to them in all conditions.
It's the pilot who decides when to stop pedalling.
You have to be pressing down on the pedal with all your strength, else you are not doing anything.
The rear pedals are not turning twice as fast as the front.
Yes, a cadence of 80-90rpm is normal.
Why change up out of bottom gear when reaching the brow of a hill? With this one there has been the view that you cannot change up out of bottom gear whilst accelerating downhill because the feet cannot feel any resistance; so one has to bring the speed down to almost standstill, until there is something for the feet to push against.