I forgot about that lol
I see it as partially making up for it, but she probably also isn't talking because she knows she can't make up for it
yeah that probably is why she didn't say anything, but still the fact that her internal monologue frames it as "I wanted to help you one last time" rather than "I wanted to make it up to you" or something is just weird.
Also, I don't get the idolisation of Chihiro in this manga. The manga acts like she's so nice, so earnest, like her only flaw is not being able to stand up for herself, But she still saw Arika bloodied and collapsed on the stairs and Ruri saying "go away leave us alone" then the next day Arika disappears besides some dodgy camera footage of someone covering their face and wearing her clothes and she decides not to tell the cops about any of that.
So she still basically covered up and looked the other way about what she knew was likely Ruri being involved in Arika's disappearance and would have helped the police investigation.
So the only way she's better than Ruri and the other two is that she didn't participate in Arika's attempted murder, she just knowingly helped cover it up.