It's not Stockholm; while she is being confined, Oliver doesn't meet the requirements as a captor to induce Stockholm syndrome, which is a mental defense mechanism. Linsday Ellis did an excellent analysis on why Beauty and the Beast isn't Stockholm, either:
https://www.youtube.com/watch?v=syYCO0QVkZo&t=779s
Pedophilia is a wibbly point tho. She's 200+ years old, but she's not attracted to him (yet), and he's 19 to her physical 15 which would probably come close to or fall under Romeo and Juliet laws. =v= Who's the pedo in this situation? I'm gonna put a pin in that and think about it later. //dead
Even if it's not a Stockholm syndrome, also she is indeed kidnapped unlike in beauty and the beast. In general terms Stockholm syndrome is when a victim fell in love with their kidnapper. It's indeed that she is not being physically abuse and being treat nicely and sometime creepily, but she doesnt have the freedom to leave either and at least I think cant leave. Actually she has not fell for him yet, so technically she did not have the symptoms yet.
Also it could be argued of why she didnt just leave or ask him if she could leave and that's idk since I'm not the author.
I'm not so fond of the idea of the ML locking the FL up until she fell in love with him. You know like the idea, I'll just lock her up because I'm protecting her. There are a lot of stories that met that requirement and it's toxic tbh. And I used to think that was really cool and romantic of the ML to do that because his love. I was a bit crazy back then and still am. But now as I'm more mature, I would be scared as hell if someone did that to me.
Also the pedophilia thing, he wouldn't know how old she is when he first saw her. Even if he knew, like would anyone believe that that is a face and body of 200+. She was also weak as hell like 60hp wtff with that. Also yeah if she fell for him it's creepy too. Mannn either way it's still a pedophilia in my eyes. Maybe this is going be like you those quotes "age is just a number". Lol, they are the main characters so they will end up together. There is nothing I can do about it. I just really like the author's other works that's why I read this. I guess this is not my cup of tea after eventhough the drawing espically the goblin was cute. ╮(￣▽￣)╭
Imo, he's not locking her up because he wants to...(?) She can't return to her castle when the king has a death warrant on her head, and the hero's ex-party members also have to capture her.
As of right now her status is technically fugitive.
I don't think hes even locking her up though. We've never actually seen him say that she can't go outside or her wanting to even go outside by her own will.
And even so she can't even go outside bc shes known as the demon queen.
Also, the timeline of the story seems to be setted in the olden days (u can tell bc of no modern tech, how the king has power and the clothing) and in the olden days people used to be able to date older people which is now considered as pedophilia.
But it was normal back then. Though the author might've put in some consideration and only made a 5yr age gap.
Locking someone up until they fell in love with you? Fell in love with a girl who look like 5? Well.... it's cute though, if you don't think about the Stockholm syndrome and pedophilia. ╮(￣▽￣)╭