- She found out the info that Grasso had a history of being a rat at the start of Episode 5.I took it as Tom telling her he suspects they have a mole, so she called someone to investigate the situation. She got the report back that Grasso has a history, so she told Tom. Unless there's something else that happened that I'm forgetting?
- She then got into the car with Grasso (and the rest of the task force) to capture Robbie at the end of Episode 5.
- She only then told Brandis at the end of Episode 6 (after she was recovering) about what she had learnt about Grasso despite not caring for it last episode.
It's a plot hole.
What makes it worse is, she only told Brandis when he went to her crib to check on her two days after the fact. So we're looking at possibly 3-4 days where she knew about Grasso but didn't tell Brandis, and only told him when he showed up at her place.
The moment she found out about the formal complaint that Grasso was allegedly a rat for the Dark Hearts in the past, she should've pulled him from the task force, or at the very least told Brandis right then.
". I knew it was over when Tom won against Perry and that face Robbie was making. 



No cuffs, nothing. Just allows him to escape.