As far as we know, Sharon was still working for the CIA when Avengers: Infinity War began, but because she also wasn’t one of the supporting MCU characters whose fate was revealed post-Thanos Snap by directors Joe and Anthony Russo, we have yet to learn if she faded away with half of the all life in the universe or if she was part of the lucky half that survived.
Unless she’s included or referenced in Avengers 4, we may never know what happened to her.
When we last saw Sharon Carter in Captain America: Civil War, she had met up with Steve Rogers, Bucky Barnes and Sam Wilson to deliver their equipment to them, and she and Steve shared a kiss.
Steve didn’t have much time to enjoy that smooch, though, as he and his allies soon had to contend with Tony Stark and the other members of Team Iron Man.