In my not so humble opinion, I thought it was done horribly. No joke, I now hate the show in retrospect, because Catra's crimes were neatly swept under the rug. I hated it so much.
You actually bring up a trope that bothers me: the idea that a female character has to end up together with someone, anyone, no matter how wrong or just plain stupid it is. Yes, I think it's sexist even when a woman ends up with another woman, because of the notion that a woman isn't whole unless she's paired up.
Before anyone gets the wrong idea, let me clarify: I'm not against romance, be it in real life or fiction, I am not out to shame anyone who wants to be in a relationship, and if you 'ship characters in fiction, you do you. I also agree with Spartan Girl that we definitely need more LGBTQ relationships represented in the media. What I am saying is that writing relationships out of arbitrary narrative obligation, shock value (Jon Snow and Daenerys, anyone?) or to make a statement drives me up the wall.
I think I read somewhere that She-Ra showrunner Noelle Stevenson has admitted that she prefers writing friendships to romance, and that's something I really, really appreciated about the show. Adora and Catra absolutely did not have to be endgame. At that point, Catra was responsible for so much shit, that if they wanted a redemption arc that badly, they should have gone the Darth Vader route and have her sacrifice herself. I know, I know, I don't like the "Bury Your Gays" trope either... but then, they didn't have to make the attraction between the two characters more than subtext. Hell, if they absolutely had to pair Adora with someone, why not Huntara or Scorpia (I loved the idea of Scorpia and Adora becoming close, but it never happened)?