What is the ruling on a girl spending more than an hour in the bathroom for meditation, contemplation, reading novels, watching videos, exercising, and eating, knowing that it is the only place available to her for that?

If you are doing these things while relieving yourself or exposing your 'awrah, then this is impermissible according to many scholars, because exposing the 'awrah in private is forbidden if there is no need for it. However, if you are doing these things while dressed, this is not appropriate; for restrooms are the dwelling places of devils, and a wise person abstains from staying there for no need. And what you are doing, from daydreaming, is useless, and a wise person occupies themselves with what benefits them in their religion and worldly life and guards their thoughts.