Zira is considered one of the most cruel villans in my opinion beaten by Broken star from warriors

BUT What if she had a reason here is my therie

First why kill a cub when your avenging a adult ziras cruel but she has cubs so who did she kill to avenge simba well that would be simbas mother notice shes not in lion gaurd or the second movie so why kill kopa

KOPA GOT VITANI KILLED DUN DUN DUUUUUUUUN

WAIT BUT SHES IN THE SECOND MOVIE REMEMBER THE YOUNG CUB

EXACTLY if the first vitani aka ziras actuall blood born daughter was in the movie or gaurd shed be kopas age not kiaras or kovus also we know shes adopted but zira and NUKA treat her like family NUKA DOESNT TREAT KOVU AS FAMILY SO HE MUST MISS HIS SISTER this could also explain why vitani isnt sad about Kopas death she never knew him how did Kopa get killed well best guess is hyenas but this would explain why she killed Kopa its sad but its the most reasonable idea sry and hope you agree