There are a couple of instances where Zira shouldn't know stuff or shouldn't be able to do what she does without being challenged.
At one point, she knows that Kiara is on her first hunt alone, but how would she know that if she and her whole group were banned from going into the Pridelands?
Also, later on, considering it was possibly a capital crime for Zira to go into the Pridelands to do her ambush, and considering that the attack was in broad daylight, not at night, mind you, and considering that Simba and Nala needed Timon and Pumba to distract hostile hyenas so that they could get to Pride Rock unhindered the day Simba challenged Scar, it seems very incredible that someone as well known as Zira could get all the way to Pride Rock to ambush Simba without someone trying to stop them.
I mean, if sneaking in was that easy, why did they need to rely on Kovu to kill Simba?
Of course, if there were insiders in the Pridelands actually loyal to Zira (perhaps they feigned loyalty to Simba to avoid being banished like Zira's crew), perhaps the Kovu thing was the main plan and they only did a distraction or whatever so that Zira could get in the day of the ambush as Zira had had misgivings when Kovu was taking so long to kill Simba.