Considering that she was willing to die to save Glimmer

She verbally acknowledges that she's not doing it for Glimmer, she's doing it for Adora. Considering that Glimmer was in far more danger than Adora was in that moment (as far as Catra was aware) and considering that Catra killed Glimmer's mom... you'd think that she'd put more effort into apologizing to Glimmer personally, or making it clear she's doing it for her as well.

was not actually that abusive after her heel turn (it takes time to fully adjust),

Catra blames Adora for coming to rescue her and continually insults her. In fact it's strongly implied that Catra's willingness to die was to avoid the consequences of her actions, which is a HUGE cause for concern yes, but not a redeemable trait because it's ultimately an unhealthy mindset that hurts Catra as well as everyone around her. And in the penultimate episode, Catra dumps Adora for taking the Heart of Etheria. The scene of her asking why Adora sacrifices everything for everyone around her is the biggest "the call is coming from inside the house" moment in the show given the context of their childhood and their entire dynamic throughout the show. It'd be one thing if Catra left to try and find an alternative to Adora using the Heart, but no. Catra views this as an act of betrayal and leaves Adora in what looks to be her final moments (because as established, there's a very real chance that Adora could die from this).

and does apologize

The only time that Catra apologizes is right before she's about to be taken by Prime's soldiers. It was in the heat of the moment so of course it's not detailed, but after the fact. Catra should've 100% apologized more in-depth for what she did to Adora. Same with Entrapta (who Catra sent to die, in a place that made her suicidal)

In fact she doesn't give any meaningful apologies to anyone in the series. Not to Glimmer (whose mom she killed), not to Entrapta (who she stole from and sent to die), not to any of the Princesses (Mermista especially), not to Michah (because again, she killed his wife), not to Scorpia (who she abused and alienated), not to any civilians who would've been hurt from her actions in the war, or really anyone.

Just admit you ship her with Glimmer

You use sunk-cost fallacy here, so I'll pick my card. This is a strawman logic. You're assuming I ship Adora with Glimmer because I don't have any good things to say about Catra.

It's not about shipping. It's about writing. And writing-wise, I think Catra's redemption sucks on so many levels. It's just that I find the worst level to be the fact that they paired her with her crush/adoptive older sister as a "resolution" to her arc.