Once they gave Naruto Sage Mode, Sakura became worthless from then on. At least initially with Team Kakashi she was a pretty important part. But Naruto just became too overpowered from there on for her to matter. Once Naruto and Sasuke faced off again after the 5 Kage summit, she realized her own weakness in relation to the two of them both physically and mentally and decided to just trust in them. It is in the manga and anime.