I totally agree that context is important. However, based on the quotes provided, it doesn't sounds like comments that could be taken as anything the least bit general.
According to the search warrant, Nicole (Lee) told Isabella that without a body the detectives did not have a case against them and the detectives would never find the body.
Nicole had also berated Lee in Front of Isabella about not being able to keep his lies straight when he was interviewed by detectives because he was dumb, the search warrant said.
Nicole stated she was able to keep her story straight and the detectives did not get any information from her, according to the records.
As you can see, her remarks sound a lot more specific than the possible scenario you suggested above, and something IM should definitely have run to police over.