Filming for the big DC television crossover event is nearing completion and most, likely, around the start of December we’ll see The Flash, Arrow, Supergirl and the Legends of Tomorrow come together to fight ‘The Dominators’. While we don’t know the plot for the crossover event, one thing we are certain of is that the rest of the heroes, aside from Barry Allen, will be introduced to ‘Supergirl’ for the first time. Given his reaction to ‘The Flash’, we can expect Diggle to be at least slightly taken back at meeting an alien, but one of the executive producers of the DC television universe has revealed that one of the other heroes won’t react well to Supergirl either…
“Part of Oliver’s [Stephen Amell] journey in those episodes is he’s kind of hit his breaking point for things he’s willing to accept. He’s had Mirakuru soldiers, the Lazarus Pit, magic, and Damien Darhk, but flying aliens who can incinerate you with their eyes is one beyond the pale for him. He’s keeping his distance, which is a very Oliver thing to do. Even Kara comments, ‘Does he not like me?’ Barry’s like, ‘No, that’s kind of how he treats everybody.’”
Arrow’s fourth season focused mainly on magic so Oliver could certainly use a break from things out of the ordinary, but being him comes with a certain element of responsibility so even though he doesn’t react to ‘Supergirl’ well, there’s no doubt that Oliver will put that aside to defeat the common enemy. Also, given that Barry has already meet Cara Danvers before, he could easily convince Oliver that Cara is here to help.
Source: Screen Crush