In Batavia, Thomas became involved with the Minahasa Unity party (Persatuan Minahasa) whose members included Sam Ratulangi. Thomas and her husband eventually returned to West Sumatra, this time settling in Fort de Kock (now Bukittinggi). In 1950, she founded a midwifery school in Bukittinggi, which was the first in Sumatra and the second in Indonesia.[19]