Comment by DatHoe on The Monster Duchess And Contract Princess - Chapter 44

She was abused and starved by her family since the day she born. They only feed her enough to keep her alive, and the things they feed is not even nutritious food that a growing child need. Her sister and her are only 2yrs apart but look at the size different. The author draw her small like a 7yrs old to indicate that she is malnourished.

A very good explanation

Or just made it simple... For example like this > She was starved, so her growth was affected