Cuteee

Both Abigail and the FL live in a fatphobic world. Even small words like when the very thin maid told the FL she was on a diet to be pretty for her date or when everytime a corset is mentioned, that they tell the women to not eat much so the corset will fit. Small words like that still stab at wounds and it's hard to just move on when the words that were given to you when you were fat, are still being given and passed around even now when you're thinner, or being told to even thinner women.

Even near the chapters at the beginning, we still see her eating less and being somewhat hypocritical even though she tells Blanche to eat as much as she wants. I don't know what chapters you haven't seen but If you've seen the brother and the tea party scene, you know that it's more than "just an insecurity" because it affects the women around her constantly being mentioned by the sexist men, and that she can't just think differently.

Tldr: the world around her is still fatphobic regardless of her being in a thin or fat body. Her insecurities can't just go away when the main reason she's insecure (fatphobic society) is still around her and pushing her to an impossible and painful standard.

Note: ik the ML said sweet words and defended her, but it'll be a long time before she really becomes confident in herself. Adding to the fact that she still doesn't see Abigail's body as her own (recent chapters show this)

I mean just because she transmigrated in a beautiful body doesn’t mean it erases the trauma, abuse and insecurities she has suffered all her life. I think it’s a realistic depiction despite this story being in a fairytale.