Ashe told her (like an eejit) in the line immediately previous, she just had to latch onto that.
Are you saying that she is so smart and cunning that she arranged blackmail, but she is so stupid that she spill the beans, not knowing what to answer, because she didn’t know that Fiona knew about it, and then she got lucky and Ashe helped her? It doesn't look real.
What Fiona would tell Delilah was as very expected and inevitable.