This may contain spoiler
It's been so long since I've read the novel but her being an airhead has something to do with her past past life that I cannot discuss here cause it's a huge spoiler but yeah.
If you want to find some serious mc find another manga cause this mc has a very good reason to be an "airhead" and only focuses on one goal and that is to pet "fluffys".
And to be honest, I would too. Specially on what happened to her past, she deserves to only care about herself in this life now.
I would say.. what do you expect from someone who has gloomy past life that can only stayed on hospital bed yet still being thankful for the hospital fee being paid and said the so called life is happy enough. If you don't like her personality again, just stick to this premise since the very beginning she was introduced this way.
And to add more detail on that, her goal in this life is just seeking the fluffiness of fluffiest from the very beginning of her second Life no other goal, no other options. Stick to these premises and you'll find the author just being consistent with her/his base story. The character development? She's being cold hearted is pretty much one of it, on note that she's not with a fluff or if anything happened to her fluff.
Also was anyone else kind of frustrated when she abandoned the dragon and was listening to anything Zakkun was saying? She's extremely airheaded and it's kind of annoying. The story overall is good but the mc has such a dull personality. She is a good person, yes. However, she doesn't listen when people talk and only has one thing on her mind. She calls it "hard work" but in reality she is just blessed with talent. I dont hate her but I think she needs character development. It also frustrates me that they hide things from her but I suppose it cant be helped because she doesnt actually care to listen when they talk. Anyways that was my opinion overall and I really enjoyed the story so I need it to get updated!! Its been a year