Why did Onin tell the Krimzon Guard about Jak's arrival?

Solution 1:

For Praxis thinking that Jak "would be different", that would probably refer to how he was exposed to Light Eco during his fight with Mira and Gol which probably allowed him to survive the experiments

The fact Onin informs the program of Jak's "Existence" would imply that she knew about his return prior which could mean that she knows more about the what occurred in the past than anyone else as she would have known about Jak's being exposed to Light Eco and that they would find the Time Gate and return to Haven

she may also know that the events of Jak 2 is in part a paradox, if Jak didn't defeat Kor his young self and Samos would have never went back in time to eventually find the time gate which allows the Metal Heads to enter the world from the future which is what led Jak back to Haven