I’m not familiar with the source comic, but I figure a few minor tweaks would have made the movie significantly better, or at least a lot less cringey.
Kara’s reasons for her drunken “vacations” needed a small expansion. It’s not just so she can drink herself into a self-pitying mess, but also because she finds Earth periodically intolerable for two key reasons - sensing too much and sensing too little. On Earth, her invulnerability leaves her only barely able to sense hot or cold or fear or pain, but her super-senses make her very aware of human sounds and smells. Somewhat akin to the 2003 Daredevil movie, she can only sleep (and she doesn’t really need to do that either) in sensory-deprivation. We get a hint of this in a momentary flashback scene where she’s standing at a window in Metropolis and uses her earphones to cover the sounds of screams and sirens and whatnot, but for me the real disappointment was that we didn’t get to see the trailer-teased moment where “your powers should be kicking in right about… now”. That would have been a prime moment for Superman to say to her “Don’t freak out”, a line that she would not have understood at the time but which she used repeatedly during the movie.
“Don’t freak out” is not a useful thing to say. If somebody’s having an overwhelming moment, telling them to not be overwhelmed won’t help, but it’s the kind of thing Superman might have said to her at that moment and which she might say repeatedly to Ruthye as shorthand for “I can’t help you with your personal crisis, but please… try to control yourself because it’s making me feel bad.” This could have come in context in a scene where Ruthye asks for help and Kara snaps at her with “I come on vacation so I don’t have to listen to people asking for help!”
Kara could get total isolation by just parking her ship in orbit around a red sun and drinking by herself, but she’d tried it and it was unsatisfactory. She grew in a crowded city (or what was left of one) and total isolation has its own drawbacks, so she needs to be around people (or sentient aliens, anyway) in manageable doses.
I have no problem with Kara being a deeply screwed-up person, considering what she was seeing in Argo City right up to the moment of its catastrophic failure and her escape, but her repeated lecturing of Ruthye about not killing for revenge ring hollow. Kara is definitely and somewhat casually killing people left and right (I guess…? The Brigands seem near-invulnerable, which makes me wonder how Ruthye was going to be able to kill Krem with a sword after he’d survived a beating by an enraged Kara), but that could have been altered slightly so Kara’s trying to not be lethal, perhaps explained by a reference to her being the last child of Krypton (Kal-El doesn’t really count, she says, having been raised entirely on Earth) and Krypton was civilized, eager to preserve life as much as possible, thus she views Lobo as a brutal and nihilistic agent of chaos. Let Ruthye have a moral arc where she ends up mentored by Kara and Lobo, presenting supposedly opposite sides of the coin, only to learn that Kara’s morality is deeply flawed because she’s deeply flawed, and Lobo does indeed have a personal code that he strictly lives by, much more rigidly than Kara clings to hers. At the climactic scene when Ruthye is about to get her revenge on Krem, Kara is encouraging her not to but Lobo is egging her on and Ruthye kills him, to Kara’s dismay but Lobo’s massive amusement.
Frankly, the whole “don’t kill him, it won’t help and you’ll be just as bad as he is” trope is such an overused cliché, I was disappointed this movie used it. Ruthye getting her revenge would have been a redeeming subversion, and afterward she says goodbye to Kara and decides to hang around with Lobo, which he’s willing to play along with (for a little while) mostly because it obviously annoys Kara and he finds that hilarious.
Kara returns to Earth for the ending chat with Superman, says something along the lines of “there’s way too much pointless brutality in this universe, I think I’ll try keeping it in check here on Earth for a while.”
“So you’re going to try being a hero?” he asks, optimistically.
“Heh, sure,” she rolls her eyes a little as she pets Krypto, but… yes.
