They only suspected the crown prince. Although all the evidence pointed to the crown prince's suspicion, they did not have any evidence. If news spread, she and Judge Wuwould both be beheaded.
In order to protect themselves, they could not speak even if they guessed the truth. However, just because they could not say it now did not mean that they could not say it in the future.
This time, the crown prince was clearly targeting her and the prince regent's residence. If Gu Qingxue had not discovered some clues and woken up the thirteenth princess, the thirteenth princess would have definitely died a few days later if she remained unconscious without eating or drinking. At that time, not to mention the empress, she was afraid that the emperor and the empress dowager would misunderstand her relationship with the prince regent 's residence.