So, I must preface this with saying that I have no prior knowledge to the Nobody GoI, its format, or 2599 at the time when I initially read this, but I still followed it pretty well. Now, after reading 2599, this article makes a lot more sense and hits home for me more.
However, I am uncertain about the use of the word "Gods", whenever 2599 is experiencing some kind of anxiety or distress. This is a very minor issue, but I think the singular "God," would work better because, to me, "Gods" has a sort of fantasy vibe to it.
My body is so stiff I can't even cross my legs easily! Later I tried to show it to Linda, but I couldn't do it.
Here I would break it up some. Add a transition between her saying how stiff her body usually is, then say something about how she tried to show Linda.
If someone gives me an order, the bird goes crazy and moves me to do the order
The phrasing here is kind of awkward IMO. I don't remember what it was like to be 14 either, but I feel like she might curse more. At least a little lol. Perhaps something like "If someone gives me an order, I have to follow it. The bird loses its shit and makes me do what they tell me", as an example.
Okay, here's what I figured out. If someone gives me an order, my body moves on its own to do the order. Even things that I can't possibly accomplish before. I never seem to do it perfectly for some reason, but that's not that important. I think if a friend tells me to be first place this year, I might just make it true.
A lot of this is implied from the previous note, where she talks about how the bird goes crazy and makes her do the order. You can also be more specific about 2599's motive behind having her friend tell her to be first. Like, "I think if a friend tells me to be first this year, I might have a shot at beating Alex" or "making mom proud". This way, when she finds out she came in second again despite using her power and trying her hardest, we feel even worse for her.
In general, the last three notes can be shortened a bit I think. They seem awfully wordy, but that could be just a personal thing for me.
I do like how you've implied that she was taken away in the middle of writing her final note though, this was a nice touch! I wish you the best of luck with your progress, author!