Chieko Kawabe began her career at the age of twelve, starring as Sailor Mercury in the Sailor Moon Musicals, Sera Myu. According to Wikipedia (the most reliable of sources):
She started in 2000, in the Fan Kansha event for the 2001 musical, Transylvania no Mori, Kaiteiban. She continued for a couple more years, appearing in five musicals total, finishing with the 2002 special musical, 10th Anniversary Special. During these musicals, she appeared in some of the more special musicals, including the Death Vulcan special revue show, the second half of the musical being an entire musical revue showing, and the first Sera Myu DVD, the 2002 10th Anniversary event. She also appeared as a musical guest for the next Fan Kansha, performing signature solo song, “Drive Me the Mercury” with the next Mercury actress, Wakayama Manami.
There are some promotional images of her featured in the programs.