If it was her acting alone without an official task assigned to her by Cerberus, then there was no way to prove that Cerberus was truly involved in it all.
They could try to confront Cerberus about it, but it was not like they could take any action over the word of a single person who gave up that information while being tortured and probably killed after that.
Perhaps they could plan to keep Ash alive as proof or as some form of bargaining chip, but it was still very unlikely that they would be willing to do anything to save her.
Under those types of circumstances, it was usually much easier to cut off all relationships with anyone in that situation, as Cerberus or any other crime syndicates would not so easily give in to any threats, even if the life of one of their people was in the balance.
