Ada theory.
Spoiler warning, if you have not completed the current story DO NOT read down:....In the Arcano story, there is a cut scene that shows Ada when the bombs fall on Arcano 4 years prior to the current story. In that cut scene she is clearly a toddler, around 3-6 years old. Ada as we see her now appears to be a mid teen, 14-18 age range. I think Ada was originally supposed to be a loli character like Truffle/Tabethe/Lisbel and I think she, like Flora, got sized up to medium female size. If the bombing happened 4 years ago, she would be only around 7-11 years old now. Which makes everything that's happened even more tragic when you really think about it and would further explain Ada's mindset and why she turned out the way she ultimately did. She's very much a Fina like character, escaping from reality in to a fantasy of her own creation mentally just to escape from the trauma.
