LE's primary purpose in setting up this meeting may have been just to see if she would agree to meet with the guy. The fact that she was -- in the middle of an investigation re her missing stepson, and after "flunking" at least one lie detector test (I think this meeting came before the second LDT) -- confirms that: 1) yes, she knows the guy, and 2) yes, she can imagine needing to talk to him about things that couldn't be discussed over the phone.
So it eliminates any possibility of her claiming "I never met or even heard of this guy before", and leaves her needing to explain what she thought was important enough to meet with him for. Yard work? Nobody will buy that -- if he'd done any yard work for her before, all she needed to do was call and tell him to come do some more -- this is hardly the time to undertake some special yard project that would require meeting with him to look at the yard together.
And who knows what she said before she clammed up -- she may not really be able to remember, since she was nervous and on the spot due the unexpected additional person. But LE has the exchange on tape, and if whatever excuse she makes up to tell in court, about why she thought it made sense to have an in-person meeting with this guy at this point in her life, isn't consistent with the conversation on the tape, then they got some good evidence from this meeting. It's doubtful they went into it actually expecting she'd talk about her attempt to hire the yardman to do hitman work.