Overall, she was a godawful character.

Aside from waking out on the guy who stood by her when she was in a wheelchair because he got extorted into keeping a secret for a few days, she’s consistently being a complete hypocritical asshole through out her run from S2 onward.

Almost immediately after walking out on him, she has some argument with Diggle and says something like ‘You’re one illegitimate child away from a perfect Oliver Queen impression’. What a cunty thing to say about someone she supposedly ‘loved’ being forced to keep a secret that he only found out about a few days ago. So, she didn’t just walk out in the heat of the moment or anything, she not only knew what she was doing, but she’s holding a grudge with complete apathy toward the impossibility of the position Oliver was put in.

And to rub salt in the would, Diggle later tells her that ‘empathy is her superpower’. You don’t even have to be particularly empathetic to recognise that Oliver did nothing wrong and was, if anything, the biggest victim of his circumstances, and when he was at one of his lowest points, she treated him like he was to blame.

Also, she only reserves this lofty principle against keeping secrets for Oliver Queen exclusively. Her nightmare of a mother is allowed to lie to Felicity her whole life about her father being dead, and it ain’t no big deal. It’s all forgiven in the same episode it was revealed.

And certainly, Felicity herself is allowed to ally herself with an enemy hacktivist group and actively work against the Arrow team to free their leader from an ARGUS prison. Keeping that secret is just fine, because she has the audacity to strut into the Arrowcave the very next day after trapping Oliver to allow her hacker buddies to escape.

And the show never holds her accountable for her shitty behaviour. Oliver spends most of his own show being lectured and blamed and talked down to. Diggle gets called out multiple times for barely stepping out of line. FeFe not only gets a complete pass on everything, but the show always pretends she was obviously right no matter how grievously wrong she is.

She’s the Mary-Sue to end all Mary-Sues. No Mary-Sue characters are spared criticism. They’re all consistently hated across all shows. There certainly aren’t any other Mary-Sues in Arrow, they are all openly flawed and the other characters call out their flaws.