Which "her"? If leafa, harold won't betray her, 100%. Justus might just tho.

😬

It is all about 'doubts'. Even if you can see the future with 100% accuracy - it is about being able to convince others that you can, in fact, see the future, and that you can do so with 100% accuracy.

He has to play his part so that he makes Justus show that he is the villain. Justus is currently is hiding the fact that he is the Villain an accord to Harold's knowledge of the game it was something like years(?) before he made a move and was nominally ousted as the Villain. He has to speed up that time line and until he has him ousted they are in a pseudo protection period. Meaning those two are largely safe in trying to directly gather information.

This can more or less be considered Harold making preparations by having others gather the information. Arguably most important thing is he now has other people that will be his 'allies' to a varying degree based on the information they gather - this opens the option that if something in the information they gather is suspect. It is unlikely that he will have to convince them of the validity of what they personally gathered and can move directly to having them figure it out on the own or have the potential to explain his situation without being sidelined be something else.

Without this, Harold's existing reputation would have him for some arbitrary reason that would lead to his own death. In a way you could say he needs to establish that he was working against Justus the whole time after being caught up in this and that, or he somehow will be labeled as an agent or co-conspirator, etc. of Justus. The KEY point is (if I remember correctly) is that he is aware of this outcome.