The Pre-Saint Realm was part of the nine levels of the Half-Saint Realm. However, it was also above them in a way, getting infinitely close to the Saint Realm.
Thus, others would have difficulties seeing how many trials one had gone through even if they had strong Spiritual Power. They could only estimate it from their combat ability.
Princess White Li was strong enough to fight with some weaker Saints, so Zhang Ruochen always thought that she'd already gone through one or two Pre-Saint Trials. He didn't expect that she was only a Ninth Level Half-Saint.
If she was already this strong, how much stronger would she become once she underwent the first Saint Trial? Clearly, the stronger one was, the stronger the saintly rules one cultivated would be. The thunder trial activated would be stronger too.