Are heroes supposed to know the trigger condition for spawning Valyndra and making her attackable or is that supposed to be hidden information?

All quest information, unless explicitly stated otherwise, is public knowledge. With very limited exceptions, a hero should be able to pick up and read tbe quest guide.

so it's not like Imperial Assault where theres specific info to be readt to the players and the rest is secret?

1 hour ago, WalderFrey said:

so it's not like Imperial Assault where theres specific info to be readt to the players and the rest is secret?

Correct. It is not like IA.