Ms. Rousseu often was in the back of the pack, riding solo, as she prefers. She has done cycling tours on her own or with TDA since 1980, but has been ill in recent years, she said. “I’m not supposed to be here,” she told me. “I prayed a lot to return to my health to be able to suffer again on my bicycle.”

She said this would likely be her final TDA ride. Some of the cyclists were too competitive, and, she said, it seemed to her that as soon as she pulled up to a Coke stop or lunch, “they jump on their bikes and go, go, go, ” because they didn’t want to arrive at the next stop after her.

A couple of days later, on our rest day in Nouakchott, I told her that I had been talking with some of the younger riders — in this case a group of men in their 40s and 50s — who singled her out as an inspiration: “Ordinary people doing extraordinary things every day,” as one of them put it.

She looked at me for a moment and her eyes welled up. She touched my arm and walked away.