Simba says in SP that he banished Zira and her cubs from the Pridelands. The official Disney story is that Zira and some other lionesses were banished for being loyal to Scar.
It could be that Zira and some other lionesses attacked Simba after he took over the throne, believing he was responsible for Scars death and refusing to accept him as king. This would give Simba very good reason to want them gone. Also, it might explain why Nala too seems to hate Zira so much. If someone tried to kill my mate, I’d hate their guts too.