From Sonic Retro
Sara, spelled "Seira" on-screen, is a sassy and cutesy catgirl featured in Sonic the Movie. She is the daughter of the President of South Island and serves as a damsel in distress in this film. Despite being a kidnapee she has a hold over Robotnik whom is infatuated with her.
Sara is taken hostage by Robotnik along with her father, the President. When Sonic and Tails arrive to save her they are given conditions on which she and he will be let go. They must destroy one of Robotnik's creations which has gone haywire, Metal Robotnik. After Sonic and Tails leave, Sara boards one of Robotniks vehicles and accidentally launches it with her and Robotnik inside. This vehicle turns out to be Metal Robotnik, and it heads towards Sonic and Tails. When it reaches them a battle ensues and Metal Robotnik is destroyed. Robotnik swears revenge but Sara curses at Robotnik and warns him not to harm Sonic.
Metal Robotnik reappears again after Sonic reaches the fortress but it crashes to the ground revealing Sara and Robotnik inside. After being revealed, Robotnik pretends to hold her hostage again and Sonic tries to rescue her but is thwarted by Metal Sonic. After leaving, Robotnik unties her and gives her a wedding dress and promises to marry her after the Land of the Sky is destroyed. She is less than happy about it and attempts to strangle him. Later, they stumble onto the Sonic/Metal Sonic battle and Sara falls out of the vehicle only to be caught by Knuckles shortly before she can the ground. The battle continues and she tries to coax Metal into stopping the battle, first by shouting then by attacking it. In the end Metal is destroyed and her father remains alive and the Land of the Sky along with South Island are left unharmed.