I’ve talked more broadly about the fatal flaw that drives Devon’s fall but I want to dig a little more deeply into the inherent subtext of gender going on with it because it’s really juicy and is a huge amount of what makes her character hit so well for me.
Devon has that streak of pride that develops into a superiority complex centering on her skill in the Force—and what is such a consistent theme of the things Maul says to her, especially in episode 3 where he is explicitly reading her thoughts out of her mind and giving voice to them, as his discovery of her name without her giving it to him reveals to us at the end?
“The Jedi were once revered protectors of the galaxy, but now they are considered traitors. Oh, how that must bite. To live as a fugitive, hand to mouth.” “Training vigorously to achieve something that few could, only to be denied. You crave that unfulfilled destiny.” “Crushed under the heel of those who are, in truth, inferior to you.”
As a Jedi, Devon’s skill and talent gave her station and respect, but Order 66 ripped that away. The destruction of the Jedi Order forced her to hide that power and that skill and pretend to be just like any other teenage civilian Twi’lek girl to survive—and that’s the thing, right? The GFFA is, for the most part, a very patriarchal place to live, just like our world. (Please do not make me cite sources for “the GFFA is misogynistic on the Watsonian level”, the sources cited are All Of Star Wars.) So: the egalitarian nature of the Jedi Order elevated Devon—and the Empire cast her down. Every Jedi survivor experiences this loss of status, but she has it worse than many because of who and what she is without her abilities or the prestige they once gave her: a teenage girl. She and Daki spent a year begging on the streets to survive; the humiliation of that and how she must have been treated in the process could not drive her loss of status in any deeper. Is it any wonder she is so full of resentment when we meet her? That she is so seething with wounded pride she has no outlet for that she won’t even give a false name when she’s arrested?
Look at how stridently Devon pushes back against being considered a peer of Rylee’s in every scene they share, how every interaction she has with him is flavored with, at best, a graciously condescending noblesse oblige—she knows that if the galaxy she lives in considers her a peer of Rylee’s then that means it actually considers her less than him, and she ultimately thinks he is nothing compared to her. Hell, go a level more abstract with the subtext: a different kind of narrative than this one about a Jedi girl falling to the dark side would take that useless boy/hypercompetent girl setup to ultimately reduce Devon to a reward for Rylee, who that narrative would deem a more deserving main character—and the specter of that concept makes Devon want to kill everyone in sight.
This is why, of our darksiders in play in this era, it had to be Maul who turned her. A Dooku type would never get to her. The Palpatine wine-and-dine that Anakin got would not work on her. But when she was cast down into the gutter by Darth Sidious she met his former apprentice who he abandoned to the same fate—who spent a decade scraping to survive in a literal trash heap and who has continued to cling stubbornly to life despite being consigned to that fate. Maul is scrappy and devastatingly honest when he needs to be and in order for someone to successfully sway Devon Izara to the dark side they needed to understand the loss of status she experienced and the resentment it festered in her long before they met. She needed someone who truly understood what was taken from her—thus, the shadow lord, the king of the gutter himself.
I must stress: this never would have been a problem for her without Order 66. Devon was a good person, Devon was happy to use her powers to help people. She would have been a great Jedi. Devon also enjoyed being praised and respected for her powers and—and is that a bad thing? Doesn't she deserve to be? Of course she does. Dark side falls in Star Wars are all about how things can be two things at once and how the line between them is so much thinner than we like to think. Sidious took that praise and respect away from her and she deserves it back, and she feels she can't get it back in her new reality by being a good person and using her powers to help people. So it is ultimately so easy for Maul to use Devon’s resentment to demolish her altruism, so that she becomes willing to reclaim her lost prestige by becoming someone who doesn’t care about who she has to hurt to get what she wants.
Because it really was such a monstrous crime that was done to her.