Several people had the same idea I did last chapter, and probably these chapters as well, but I'm also leaning towards Kubaru being an unreliable narrator and her wounds being self inflicted, as we never see her actually interacting with her (supposed, at this point I never know) real father.
This would tie into chapter 24 where we're shown how easy to manipulate Tomata is. When he hears a sob story he turns into people pleaser mode, even to his own detriment, and will do what he can to help, and I think it's very possible, even likely that Kubaru saw that side of him and figured she could make use of it, turning him into her new dad, one she can control and who will always do everything for her. And we know later he took over the company and essentially does her bidding from behind the scenes, so that checks.
Anyway I guess we have a murderer on our hands now woohoo!
4 more chapters until we catch up!
PS: Kubaru with dark long hair speaks to me. I know the author mentioned in one of the early afterwords that he drew her like that in the present as well but then changed it to the design we see today. I think I wouldn't have minded her keeping the long hair but who knows.