You have to realize -- Hillary is (or was!!!) about to walk into an interview and has no idea the extent of what they know or are seeking, and by extension how much risk to take. A wise lawyer would absolutely tell her to take the 5th at this point, and it's going to look horrible if every answer is "I don't recall." Things change further if the invetigation is in fact scoped on public corruption, or if the FBI has retrieved the emails she deleted and is targeting specific lines of questioning. Lynch has all of these answers and could steer the Clintons toward or away from a strategy.
This is why the meeting was a giant breech of ethics. Any inside dope, even a head nod as to whether they have a smoking gun or don't is of major value to Hillary when deciding how she walks the wire.
FBI must be furious!
And why a private meeting at an airport? No records, plausible deniability (if in the worst case they were caught...whoops!)