@Autumnbear As someone who has seen malnourished, abused and otherwise damaged children, i can confirm that they do indeed look like Leslie. Her size is nothing unusual for being malnourished and emotional growth is extremely uneven in children who are mistreated. They only learn what makes like easier and fail to learn all sorts of things a "normal" child their age would naturally understand without being told.
The "Maturity" of people in general has virtually nothing to do with chronological age. Its a mix of inherent qualities, experiences and general formation during early childhood. Talking baby level formation. The most important time in a persons development is when they are too young to select what they absorb, when they have nothing set and are open to everything. You screw them up then and it manifests in the years to come. The "terrible two's" are often the first sign of this as the child is only just capable of expressing itself in any real manner. People often misunderstand and think its all just normal, like how they say "teens rebel" is just a thing that happens. Teens don't rebel unless something is wrong. When they become teens they just gain the burst of agency and hormones that allow all the shit going wrong in their life to come out into the world. Its all just misunderstanding of the causes and trying to band aid everything when shits already gone wrong.
Australia is literally burning right now because the people in power won't clean up the stuff that catches fire BEFORE it catches fire. The country catches fire sure, but it doesn't have to catch fire where you live. If you let the country just do its own thing the entire landmass will explode in hellfire the likes of which humanity has not seen in tens of thousands of years. So instead of preventing this the government just acts like its normal and unavoidable while fighting the result.
Anyway i went off track there but i hope you get my point. Leslie is a kind child by nature sure, but apart from that everything is perfectly in line with what an abused child would be like. Her torture only increased her sensitivity to suffering. Also she missed most of her growing years thanks to lacking food so she should be extra frail. This was a from birth kinda thing.