I'd also like to point out that IMO we do not know where the mystery car was during that Starbucks ride: nowhere to be seen (presumably still wherever they "spent the night"), already waiting for her somewhere else (like en route her normal way), or actually following her during that. I hope the LE does know that.
What is more, I do not know if Liz 1) got Starbucks on normal work morning as well or not 2) if she did, did she do it on that same time as on the day she was killed 3) if she did, did she normally come back home with the drink and left for work afterwards, had her drink inside Starbucks, or started driving to work with her drink.
If any of that has been discussed by her parents or S, I'd welcome to see their interpretations on that.
I agree that if choosing a place to kill someone early in the morning, then a coffee shop of all places would not be the place where I would think there would be no witnesses.
Then again, when choosing a place to park my car before the murder, then a school of all places would not be the place where I would think there would be no cameras... so clearly I cannot think like that killer!