So many alarming things about this whole thing.
My first thought was an emotional breakdown, after the trauma of losing such a close family member,on top of exams and an upcoming wedding, that also involved travel, expense, time away from work and school. And grief, it can make you behave in ways that are not always in your best interest.
But it's clear to me there is something much more sinister going on here. I don't find it so unusual for her to meet up with someone before heading to her house after her flight, no matter the time, she may have wanted some down time, or even some space to not think about her loss, before heading home. It's been stated that this was traumatic for her. The fact that this person has not, as far as we know,come forward, is very telling.
And trust me, the dude you buy your weed (Or whatever) from is not going to meet you in a park in the middle of the night and then give you and your luggage and your bag of weed(or whatever) a ride home. Ridiculous.
If it was someone who was doing things they shouldn't have been doing, they could have quietly gone to LE and cleared themselves and requested their identity be withheld. LE could say, we have ID'd the person met in the park and this person is not a POI or suspect. Period, the end.
This was someone she knew well enough to meet in the wee hours in a park, and willingly get into a car with and didn't indicate any hesitation/distress per the Lyft driver.
As others have said, I also have did some incredibly stupid and dangerous things in my 20s, but I wouldn't have met someone in a park at that hour unless I was really comfortable with them. Really really comfortable. Even grief stricken, if it was a stranger, that's be a big no.
All MOO