A Knight of the Seven Kingdoms - S8-E2
Continuity mistake: During the battle strategy meeting around the table, Sansa wears the long silver chain and circle neckwear, and the long chain changes the way it is placed through the circle. Sansa's chain is put through the circle in a way that's over and under in most shots, but when Jon explains that if the dragons are in the field they won't be able to protect Bran, the long chain is put through the circle the opposite way, under and over. (00:30:05)
A Knight of the Seven Kingdoms - S8-E2
Continuity mistake: When Gendry gives Arya the dragonglass weapon that he made for her, in the following shots Gendry's leather cloak straps switch between being crossed with his left strap over the right strap, or his right strap over the left strap. (00:43:00)
Answer: Daenerys and her allies don't just want to kill Cersei, they want to claim King's Landing and free her people from Cersei's grip. The problem is the people of Essos viewed Daenerys as a liberator but the people of Westeros view her as an outsider and usurper. They would never follow Daenerys if she had Cersei assassinated. That is Daenerys' dilemma, she certainly has the ability to wipe Cersei out and obliterate her armies but doing so would make her a tyrant. Which as it turns out is exactly what happens.
BaconIsMyBFF
But no-one has to know that Cersei was assassinated. Arya has the ability to impersonate anyone she kills, so she could pretend to be Cersei afterwards and profess to the citizens of King's Landing that she has yielded the throne to Danaerys and that she is going into exile.
Phaneron ★
That plan would be incredibly suspicious. Knowing what they know of Cersei it is highly unlikely the people of King's Landing would believe that she would accept defeat so easily and then voluntarily exile herself, never to be heard from again. In order for that to work, all of Cersei's advisers and closest allies would have to be similarly eliminated, or they would have to be on board with the exile plan. If they are all killed it sort of makes it obvious that something is amiss. There's no way they would be fooled by Cersei suddenly doing a 180 and completely changing her personality by accepting defeat without a fight. If any part of this plan goes wrong then Daenerys would look worse than just an assassin, she would also be deceitful to the people she hopes will willingly accept her rule.
BaconIsMyBFF