
Have you considered these possibilities?
1. She will still have the same body type? Just because we have seen her baby body doesn't mean she'll stay the same. She could have looked like that as a baby in her past life too. Or she could develop to look like her past self.
2. That her weight from her previous life was influenced by her stressful surroundings? Stress can make you gain weight faster. She could have had a eating disorder. She could have had parents with the same body type as her in her past life and now her genes are different so her body is different. Any of those reasons would cause it to make sense that her body changes.
Without the genes or stressors in her life it is obvious her body won't be the same. All of that is not even considering the fact she could have had a bad diet in her past life. Which is a possibility since she would have had limited money and would have to depend on cheap foods which tend to be unhealthy. ┗( T﹏T )┛ just saying
I think that instead of reincarnation, perhaps had ara in her own body travelled to a different dimension, that would be cool. I mean, I'm not complaining, I love the story, but I would really enjoy a webtoon like this with a larger person as the protagonist. I don't see why the protagonists always have to to change to become more physically appealing. I know that's just how it goes and this isn't meant to be realistic, but I'd love it more if they could learn to be appreciated for who they are no matter their looks :)
Just a side rant, sorry.