Either she could take the money she earned already or she would take on the next stage of the task too which would result in much greater rewards.
Ash had already been heavily involved in the investigation part of the quest so she already knew quite a lot which meant that she could be useful in carrying out the follow-up task.
Perhaps if she had not taken such initiative when doing the task and did not perform so well then she might not have been given the second option but it did seem like she had proven herself to be somewhat capable that Ross was willing to take a chance on her.
While she was being allowed to do more to prove herself and to earn more money, Ash still needed to think clearly about whether she thought she would be able to handle taking on a task that required more of her.
