They (being tandems) DO take some getting used to, for both the Capt + Rear Admiral. I hope you (plural) are able to give it another try. Without knowing if there were particular aspects of it that she didn't enjoy, it's a little hard to offer much other than general encouragement to take it easy, give it a couple tries before hanging it up, and +1 to LOTS of communication. It takes a while to be able to ride together smoothly. I've often compared it to being in a canoe together, or ice skating arm in arm, or dancing really close together. It usually starts out VERY tippy, and every move that either of you makes rocks the other one, which is usually pretty unnerving. You gradually learn to move less, communicate more, and "trust" each other's movements ...
Anyway hope you + she get another try + come to enjoy it together.