How did Glinda and other citizens know that Nessa was the WWoE?

The whole 'Nessa shrinking Boq's heart' was in the Governor of Munchkinland's office with only Elphaba and Nessa to witness it. How did Glinda know that Nessa had become sort of evil because of love(kind of like Anakin from Star Wars)? Also how did Glinda and other people celebrate that the Wicked Witch of the East, not the Governor of Munchkinland has died of Dorothy's house?