Complex sentence: In 2006, G.E.M. entered a competition called "Spice it Up" where she won first place and was noticed by her current manager, Tan Chang, who offered her a contract with Hummingbird Music thus becoming a professional singer at 16.
Split into simpler sentences: In 2006, G.E.M. entered the "Spice it Up" competition in which she won first place. She caught the attention of her now-manager, Tan Chang, who offered her a contract with Hummingbird Music thus becoming a professional singer at 16.