The new Green Arrow's identity was kept secret throughout the first half of Arrow season 7, and the show threw people off because they had someone completely different in the suit all along. It was speculated that the new Green Arrow was Roy Harper, while some fans believed he was a future version of Oliver's son, William. However, none of these theories turned out to be true, as it was later revealed that the new Green Arrow is Emiko Queen. But one problem arises with the appearance and build of the new Green Arrow being radically shifted after her identity was revealed.
The Arrow season 6 finale left Oliver Queen exposed as the Green Arrow and sent to prison, which caused Team Arrow to break up and move on with their lives. Vigilante activity in Star City all but vanished, with the exception of a new Green Arrow who emerged in the Arrow season 7 premiere. Like season 1 Oliver, the masked archer has a list of enemies to kill. So far, the only characters interested in assisting the Green Arrow has been Rene and Curtis, who are desperate to get back into action. The Green Arrow's identity remained a well-kept secret throughout most of Arrow season 7, and one of the reasons people weren't able to pinpoint the identity of the new Arrowverse superhero was because Emiko wasn't actually in the Green Arrow suit all this time.
Now that the audience is no longer in the dark about Emiko's identity, the series has adopted a new look for the archer. As of the Arrow season 7 midseason premiere, the new Green Arrow's female physique is more prominently on display. In many scenes, she didn't bother to wear her mask and the way her costume was fitted to her body made it obvious that the new character is female, which was a surprise to Oliver. It's easy to understand his surprise, however, when looking at previous episodes, in which the person in the Green Arrow suit was clearly male (or, at least someone with a bigger build than Emiko Queen actress Sea Shimooka.
The first half of Arrow season 7 carefully concealed Emiko's identity by hiding her feminine build. While it may certainly seem dubious on the part of the show's producers, it's actually something that happens quite often in Hollywood, as actors and actresses sometimes aren't cast in their roles until later in the seasons; there's also the possibility that Arrow's creative team wanted to lead fans in one direction only to drop a bombshell like Emiko Queen being the new Green Arrow at a later point.
Interestingly, this isn't even the first time that the Arrowverse has done something this. While Arrow's Prometheus reveal made sense as the stunt double in the suit was also male and fit the same body build as Adrian Chase, the other instance in which the Arrowverse tricked people was revealing the person Zoom kept locked up throughout The Flash season 2. The person in the cage and the person Team Flash saved clearly weren't the same. Overall, though, it's quite clear that Arrow's writers were aware of who the audience would suspect the most as being the new Green Arrow, particularly when Felicity gives voice to a fan theory by wondering aloud if the man behind the mask is Roy.