@Ryrie - Thank you! If you didn't bring it up, I would have.
I suspect the author is dangling this role reversal (one where the MC saves the shitty childhood friend once he realizes she isn't just being an idiot but is legitimately in a pinch), to setup some character growth, an apology, and potential reconciliation from Koharu.
That said, if the author expects most of us to even consider rooting for Koharu, that better be one helluva groveling apology where she owns all of her bullshit and swears off the violent tsundere schtick forever. Oh, and she explains why she didn't reach out to make amends sooner. And pays to fix the door she and yuri loli friend destroyed.
With this chapter, we see that beneath his usual antisocial, edgy turd persona, Tamaki is actually a good guy who wouldn't abandon someone in trouble; even someone who has wronged him as much as Koharu has. That is likely what he was like as child, and who he is really is at heart...buried underneath his fear, distrust, and animosity towards other people because of the trauma he suffered. Koharu now looks even worse by comparison.
Hopefully, the author is wise enough to give her enough self-awareness and introspection to realize how shitty a person she has been, and she vows to change; if not for the sake of winning over the MC, then just to be a decent person going forward. Especially when the competition, Lemon, is so far ahead of her, and is clearly the catalyst for Tamaki starting to come out of his shell.
Here's hoping we won't get some cliched, last minute flashback that glosses over, minimizes, and/or lazily recontextualizes her actions to try to justify them. "It was an accident, I was too ashamed to say anything at the time, and I didn't know how to approach you to apologize once I finally pulled me head out of my ass" will not cut it with me.
You don't get to act like an entitled brat, whom kicks the person SHE wronged in the FUCKING BALLS, without showing a SHRED of REMORSE or offering up a COMPELLING EXPLANATION. Let the bitch work to redeem herself and EARN her happy ending if she wants it so badly.
That said, experience has taught me not not to get my hopes up prematurely.