I believe another female was also imported with Marraquie, although she died relatively soon after arrival, meaning that there were ultimately only three founders. After Shani was born to Nambala and Nyeri at Taronga, she was transferred to Dubbo as Marraquie's breeding partner, resulting in the birth of Binti.
Ultimately, this meant that all Australian-born calves have been descended from Nambala and/or Nyeri, rather than having two unrelated pairs and the potential to breed a second generation without inbreeding which was originally intended.