When my wife started riding a tandem with me, she has never really ridden a bike in any real world situation. She had absolute trust in my choice of equipment. I went quite conservative (32c tires) and we never had a catastrophic equipment failure and only crashed once at low speed in 20 years. That low speed fall (going around a corner at low speed up a hill, invisible road grit) affected her confidence in my bike handling ability for months. My suggestion is to be conservative in your equipment choices and riding. One bad crash can make her decide to stay off the tandem forever in addition to whatever physical trauma.