Tell her to decide what she wants to learn and learn that, using school as a resource and other resources as appropriate; tell her to judge her own success by her own measures and not pay too much attention to external measures like school marks. (Pragmatic exceptions allowed for where marks have consequences that matter, but she should regard these explicitly pragmatically, not as a measure of herself.) It's OK to decide to put less than full effort into something if it frees effort for something more important (even if that's writing bad poetry, within reason!)

Email: my username, followed by 2, at google's mail