Zira had been a thorne in Scar's side for a long time. She was excellent when Scar had first employed her at Pride Rock LLC, but her obsession with him was downright creepy. Perhaps if Scar had been more tactful in handling the situation, things could've gone much smoother, but after she tried climbing the corporate ladder by baby trapping him (a VERY bold move considering Scar had never even slept with her), his hand had been forced. Zira was promptly fired from Pride Rock and blacklisted from the medical industry. However, banishment didn't do much to dissuade the lioness. She would go to any extreme to claw her way back into Scar's life, including using her own children as accessories in her schemes.
Kovu was the perfect candidate. Unlike his "politically conscious" sister, and drug addicted brother, he became a popular athlete at a well respected college. His future was looking bright, and after blackmailing Scar into letting Kovu become his protege at Pride Rock, there was no doubt in Zira's mind that he would grow into a brutal, cunning businessman. Unfortunately for her, this would backfire, as it would just lead to Kovu becoming really, really, really, REALLY gay.