There will be more of Agent 13 in the next film, these same writers needed just one film to show us Peggy/Steve and they did a great job with Nat/Steve friendship, so in one film they can make Sharon/Steve happen. I can´t judge the character or the acting, because I compare her introduction to the same that BW had in IM2... and in the comics isn´t Sharon supposed to be helping Cap find Bucky, alongside with Sam? of course in them she is still an SHIELD agent, but for the MCU, she is CIA, that will probably tie her with the guys to find Bucky and face whatever anything else they will have to face, while Steve and her flirt like they did in the hallway of their building :P