Oof, surprise hit to the feels. I thought Sasha would either get caught up in the book writing club, or come down more strictly on Diana's unladylike interests, but instead she was just sad about Diana feeling like she has to put on a face for her parents and having nobody to pamper her.
If Cain was around, Sasha probably would've been way more strict about this, knowing that Diana would get more than enough babying from him. But when Sasha learned that she only felt comfortable around Ilvareno (who is, at best, a playmate, and not a caretaker) she realised that she was the only one who could offer Diana the comfort she needed, and that role was far more valuable than the stern governess she initially tried to be.
Not only is this incredibly heartwarming, it's also feels surprisingly real - of course a grown woman isn't going to be led around by the nose by a couple of kids, just because they showed her a story they wrote and put on a little play for her. That would only happen in a children's storybook (or a comedy manga). A good nanny would, however, know that there's more to a child's development than forcing them into a societally acceptable mould, and sometimes, playing along with a little bit of silliness can be far better for them.
Not to mention, Sasha clearly recognises that, for all the complete nonsense of a young girl having a secret life as a superhero crimefighter, it is giving Diana all the motivation she needs to focus on her studies and learn how to be a proper noble lady, so who cares if she wants to play at knights in private? Let the kid be a kid for once. She's clearly behaving properly when she needs to, and she'll more than likely grow out of this herself, eventually.
What a good development. I really expected the story to treat this a lot more lightly, but this was a really nice way of resolving things. Thank you for the translations!