Why does Delia need forgiving? She's a victim here.
Because if Sylvester hadn't planned ahead, Delia's actions would have directly led to Myne, her retainers and her entire family being executed for what happened in the temple. Not to mention she broke Myne's trust.
Good intentions and being manipulated can be mitigating circumstances one can take into consideration when determining whether to punish someone, but that doesn't mean you have to forgive them for putting you and everyone you love in harm's way. You could argue that Delia deserves mercy; and she's given it by showing she means no harm to Myne by passing through the shield, but that doesn't mean she deserves forgiveness. This isn't like with Gil who refused to do his chores, this is Delia putting everyone on the executioner's block.
Both of them have made the decision to prioritize what they care about most above everything else. Delia chose Dirk, and Myne chose her family, friends and her retainers. Delia removed herself from that group when she betrayed Myne and put them all in danger. She crossed over the line Myne has drawn in her mind and she's not someone she has to protect and care for anymore.
Myne may not be from this world, but she has to live in it now; and she's adapting to it even if the readers aren't. She can't afford to apply the morals and ways of her old world to this new one, especially since she has neither the power nor authority to back it up. RIght now she has none at all as a commoner, and even as a noble's adopted daughter there's always someone higher up; be it other nobles or the royal family. You do what you gotta to do survive, and cutting off people who stab you in the back is one of those things you gotta do; not accept their apology and welcome them back into the fold.
Not that Delia has actually apologized yet, mind you.
...She could have talked to Myne, you know. Could've avoided this entire thing. But she didn't trust her, and this is the result. It sucks for Delia, but actions have consequences.
