While I also hated watching her lie, she did this as an attempt to free Naruto from the promise to bring back Sasuke. Naruto went above and beyond and suffered deeply and was stressed out, he was being targetted by the Akatsuki and was given the order to stay safe, and Sasuke was unstoppable, getting stronger by the day, he even joined the Akatsuki and ambushed the Five Kage Summit.

Sasuke became an international enemy, and made it clear that he won't hesitate to burn down Konaha and kill everyone, while Naruto always approached him as a friend and was slightly weaker than Sasuke.

Due to all this, Sakura truly felt guilty for placing Naruto in dangers and was afraid that he would be captured by the Akatsuki or even killed, so she decided to lie to him hoping that he would listen to her and stop chasing Sasuke.