Why didn't Orihime use her powers to reject the creation of the Espada? I finished the Hueco Mundo arc, up to episode 190, and I have a question about Orihime:

If Orihime can reject all things, why didn't she reject Aizen's creation of the Espadas? She can just say "I reject" and then cast at the Espada. POOF, gone.
Because her power is limited.

Rejecting the Espada's creation would mean changing very powerful things, beings with extreme spiritual power would vanish.

She doesn't (yet) have this kind of power. She can't reject events of that magnitude.

She can reject an injury (and even that to some degree, as shown with Ichigo's cero-inflicted wound by Ulquiorra, she couldn't reject such a powerful event), and she can reject incoming attacks (again, to some degree. Yami in his weak form was able to break it with his finger).