You could change the punctuation but I prefer This journey, unprecedented at the time for a European woman, was made 13 years after her first encounter with the disease. I don’t like the suggestion of “once”. Everything was once unprecedented. This conveys more clearly that she was the first.

Is there a *better* way to write this sentence? I would just way: This *once* unprecedented journey for a European woman was made 13 years after her first encounter* with the disease. *By encounter, do you mean diagnosis? Encounter would imply more of a witnessing.