Kiara had predicted that Arlong would not accept the special recruitment offer given to him. Even if he did, his comrades from the same cohort would not be pleased, as everyone had come through assessments. If Arlong was special recruited because of his heroism, it would inevitably lead to some dissatisfaction.
Moreover, since Mario Yuno is Arlong's brother-in-law, if someone were to gossip about this in the future, they might even speculate Mario Yuno contrived the heroic incident just to give his uncle a leg up.
Arlong gathered evidence for Kiara and got injured while performing a heroic act, so Mario Yuno's decision to offer him a special recruit was not undue. However, for the sake of her brother's future, Kiara chose to extend the assessment. After Arlong helped her with the evidence and returned, he just managed to participate in the assessment. Whether he could stay was up to him, and surely enough, Arlong did not disappoint, scoring a good rank.
