I'll take your curiosity about other's interpretations as an excuse to give my personal literary analysis on this story (though, quick warning, I touch on some pretty heavy topics here about child abuse, ableism, and suicide).
This story is, in my interpretation, ultimately one about neurodivergency in youth and how some parents of neurodivergent folks tend to react. While, of course, the neurodivergency the main character has is never specified, it doesn't really matter that much which one. Many, many neurodivergent kids can be seen to, in the parent's perspective, "lash out". This lashing out could be a symptom of underlying mental illness, or perhaps an autistic meltdown or sensory-related overstimulation. Again, that's never clarified, but it's clear that's the case, considering that the story notes how frequently this has happened, and how the mother has tried to "correct" their child through more and more desperate and severe means.
This is even more clear through the "monster" thematics. Neurodivergency is often seen as the "other" in a terrible sense, and some parents of neurodiverent children don't know how to handle the fact that their kids have this sort of disability. As already mentioned, the mother has attempted to "correct" her child through more and more severe, and often abusive, means. The child and the princess, as many neurodivergent kids do, identifies that their parents do these things such as locking them away in an attempt to hide their neurodivergency -- either through telling others that their child is normal and perhaps even better than other people, or by trying to correct their behavior though punishment. But the parents do this without realizing that they are, ultimately, abusing and hurting their children. It's a sort of violence done out of love, or a misunderstanding of how their children should be, taking drastic and harmful measures towards them instead of giving them accommodations and the help they may need.
The ending is intentionally vague, I think, but either way, it connects to this sense of escape. Neurodivergent kids who are treated like this have an intense and overwhelming urge to escape. It could be running away, committing suicide, attempting to get themselves taken away by CPS, etc., but either way, that is what the ending connects to for me.
Sorry this is like nightmarishly long! I just wanted to infodump how I took this story, especially as someone who is neurodivergent and read this with that sort of POV.