I, too, wonder how Danielle ended up in the company of the SG (if that is actually the case as this has not been confirmed) that Friday. All LE has said is that he and Danielle were acquaintances; to what degree, as you pointed out, they have not said, and it's something I keep going back and forth on.
If they were well-acquainted -say, they had exchanged each other's numbers for whatever reason-, and had mutually agreed to meet as Danielle left the office, why on earth would the SG agree to show up in the parking lot of her work, yet not drive away in his own vehicle? Sure, anything is possible (e.g., he could have taken a bus, Uber, gotten a ride from a friend, etc. ... none of which is likely, IMO), but if they were regular, ordinary friends, wouldn't it make more sense for them to have met at her apartment or his house?
To me, it makes more sense that the SG would have forced his way into Danielle's Jeep if he was indeed already inside the vehicle as it left MetLife ...
...Yet another possibility is that Danielle drove to the Berkley house willingly - for whatever reason (though not confirmed, I do believe that she was there due to the number and types of items taken from the property). There are a couple of things that support this scenario in my mind, one being that it appears LE had the SG on their radar within days -if not hours- of Danielle going missing, and two, perhaps her friend wasn't immediately alarmed because Danielle had told her she was going over there to see the SG before coming over to her house.
l