Also, my take about erika feeling like she had no right to confess was because she had ulterior goals for aya and koto getting back together. She knew it wouldn't work out between the two, and she was hoping it would finally get koto to move on so she could confess.
Another Erika's defender trying to find a way to excuse the terrible thing she had done back in middle school lol.
Let me remind you. Erika has been tormented by her guilt in the past seven years. You can see in chapter 8 she also didn't think she has the right to confess when she and Koto were high school students.
the only 'terrible thing' erika did in the past was make a wish that someone they are jealous of/angry at disappears lol. What angsty teen hasn't wished someone would disappear. If your whole argument is based on the outline of her possibly yelling at aya and that wish, then there is a million different things that could mean, and each have just as much validity. Maybe she went to confront aya first, got in an argument, then in anger made the wish after, and the argument kept aya from going to tanabata who then gets whisked away. maybe erika made the wish, went to confront aya, then a pack of controlled dinosaurs time hopped and grabbed aya and time hopped again with her. maybe erika is secretly part of some magical galactic task force and enlisted aya who then left to fight space crime.
Point being, there is literally not enough information yet available to know what really happened. Erika was not acting like a guilty assailant/murderer when aya returned. in fact, erika was not acting guilty at all at aya's return. why would she ask her dad to let aya stay with them her first night back or say "i was convinced that she was still alive" if she had anything to do with aya's disappearance/murder? followed by asking where aya went after their conversation, an obvious reference to the confrontation aya doesn't want to remember.
Just because there's no evidence something DIDN'T happen, doesn't mean it did. You need to include all context clues that are there leading to other conclusions first. Putting something in that had 0 clues, foreshadowing, context, that goes against all previously established personalities just for the sake of having a hidden twist is terrible writing. Show me exactly where erika's murderous bloodlust was established then i'll consider it. An accidental murder? MAYBE. But for accidentally murdering someone erika sure seems oblivious to having done it in both her thoughts and actions. You'd think she'd be a BIT more panicked that a person she murdered, whether by accident or not, suddenly comes back and might out her.
Sometimes a horse is just a horse.