The balcony is a place where Pheoby feels safe. It is on the balcony that she can expose her thoughts without fear of judgment, where she can tell the true story about herself and where she is protected from the prejudiced, misogynistic and invasive society with which she has to live.
The balcony is therefore a powerful place, where Pheoby can be herself, without fear of judgment, disadvantage and reprisals.