Just to clarify:

The point of female ninja (kunoichi) is to manipulate and deceive.

Sakura was trying to deceive Naruto into thinking she liked him back romantically so he would come back to Konoha with her so he would be out of harms way.

As we know, Naruto is the vessel for the 9 tail fox demon and the Akatsuki wants him for this reason, to take said fox demon and ultimately kill him in the process. Sakura cared enough to make a plan that would sacrifice her own feelings for Sasuke to try and get Naruto to safety.

To break it down, Sakura was thinking that if Naruto is out chasing after Sasuke because of the promise he made (of his own free will) to her and got hurt or killed, she would be heartbroken because he is one of her best friends.