If I remember correctly I think they said in that world she could only affect herself with that power, and it has a limit to how much power she can give. The only way she could change that world entirely is from the real world where she originally wrote the book. Which is what happened in the end.
but still , why not just to wish for magic power for herself that is , not super strong like she can wish to have power not only create fire but also can manipulate fire
shit would've been messed up anyways i think. you can't really alter the laws of that world, she mentioned that. If she did stuff wouldve prolly collapse earlier.
i just want to ask the power of her book is to grant everything that she wish for as the author but why can't just wish a magic power strong enough to defeat everyone in that world that make me confuse and somehow frustrate i know the s good but maybe she have other power then have the power to make everything for her