She began in broadcasting when she was hired by government-owned MBS-4[4] as a newscaster after being discovered in an audition in RPN-9 by its network's news director Edwin Fargas.
[6][7] She joined ABS-CBN Corporation for a decade since 1986[5][8][9] — at that time, the network was newly-resurrrected[7] and the station shared the same building with Channel 4 which later moved to its present site.
[12][13] Meanwhile, she co-anchored the network's primetime newscast Balita Ngayon;[7] and gained fame being one of the original anchors of the replacement program TV Patrol, which was premiered in 1987.
[16] She was the first to conduct exclusive interviews in 2001, especially of former president Joseph Estrada in the beginning of his detention in Camp Crame, and of his successor Gloria Macapagal-Arroyo upon her declaration of state of rebellion following a a siege near Malacañang.
[10] She has four children,[8] including musician Wency Cornejo (best known as the lead vocalist of rock band AfterImage which was active in the 1990s), as well as Ana Teresa, Melanie and Jose Miguel.
[22] In 1997, Tiangco underwent angioplasty after suffering a massive heart attack, with a huge amount of blood being replaced to survive.
[20] On January 16, 1996, ABS-CBN suspended Tiangco for three months without pay as co-anchor of TV Patrol and Mel & Jay (then a radio program on DZMM)[23] following her appearance in a television advertisement for Tide in December 1995, allegedly a violation of an earlier-issued circular prohibiting news personalities from doing so[24] without the network's prior approval,[23] which was considered a breach of company rules.
The parties executed and signed a partial settlement agreement, dated December 15, 2011,[30] wherein Tiangco agreed that ABS-CBN paid her in full the amount covering specific monetary claims.
[26] The CA upheld the said decision on August 6, 2003,[26] citing lack of evidence that Tiangco violated the prohibition upon her appearance in the commercial, justifying her unilateral action in dissolving the agreement, and considering the fact that Sonza is redundant without her in the show.