Why did Tissaia de Vries commit suicide after the coup on Thanedd Island? That happens as Geralt and Dandelion talk about what happened after the coup. After every part of their conversation there is a sort of flashback on things that happen.
‘Not one of the sorcerers changed their mind? Not even when Nilfgaard was beating and burning Aedirn, no one abandoned Vilgefortz and joined Philippa?’
Geralt was silent for a long time.
‘I don’t believe it,’ he said finally very silently. ‘I don’t believe that none would reject Vilgefortz, when his true motives and consequences for his betrayal came to light. I am, as is known, a naive, stupid, anachronistic witcher. Perhaps that is why I cannot believe that none of the mage‘s conscience awakened.’
They discuss whether any of the mages felt any sort of remorse for the happenings in the coup, and then the story goes straight to a flashback where Tissaia slits her wrists.
Why is that? She shouldn't feel any remorse as she was neutral and didn't betray the Brotherhood of Sorcerers. It just doesn't makes sense for her to do such a thing.