It doesn't appear that ML was into drugs, but it's one of only two reasons I can think of for a 3:00 a.m. meetup in a park. Complete Speculation: If she was in fact using, or was just looking for a little something to get her through midterms that week or even work or school the next day after a late flight, it might explain the encounter on her part. After a delayed flight, emotional weekend, and staying in what residents of her hometown call "Mayberry by the Sea", maybe she had been without the entire weekend and needed to get her hands on something.
We know that ML's flight was delayed arriving SLC about 30 minutes or 2AM arrival, and that she had checked luggage to claim, and that she arrived Hatch Park via Lyft about 3AM.
ML's friends describe her as nurturing, care-taking, mom-like, wanting to feed you -- making sure you have a drink, etc.
In one word, I'd say accommodating.
Viewing map routes below, Hatch Park is not even a midway location of convenience! After a late night journey, ML still traveled the furthest to meet AA - again, most likely to accommodate him, being true to her nature.
Since AA reportedly once lived across the street from Hatch Park, he's likely the only one of them known to have a history with Hatch Park. (Park is 9 miles out of ML's way - and far past AA's home).
I believe ML likely traveled to Hatch Park for convenience only, and lured into thinking their ultimate destination was a residence near the park -- someplace AA had already been waiting for her at.
I'm more inclined to believe ML thought there was a summer party taking place near the park, than a drug purchase. I think ML wanted to be around people when she arrived SLC more than she wanted to score something for just herself.
MOO
1). Travel time from AA's residence to SLC Airport is estimated at 5-6 miles, or 7-9 minutes, depending on route.
2). Travel time from AA's residence to Hatch Park is estimated at 5-6 miles, or 7-10 minutes. (Park is north or opposite direction of airport).
3). Travel time from SLC Airport to Hatch Park is estimated at 10-14 miles, or 17-18 minutes.
4). Travel time SLC Airport to Trolley Square area (near ML's apartment) estimated at 10-13 miles, or 15-20 minutes.