I think we can all pick up from what is NOT being said that no one close to the case is mystified or concerned that Toni was in this park at this time. They seem to know exactly what she was doing there, and that what she was doing did not involve someone who harmed her. Although it seems a little early, her parents are convinced enough by the evidence to commit to the "no foul play" verdict. There may have been evidence among the belongings found in the car that verified the reason for her being in the park, along with the testimony of the person she was supposed to have been meeting and/or phone communication evidence we haven't been privy to. We may never learn those details, because they may not be directly related to her death after all.
Also, her reason for being there (whatever it was) does not make her death any less tragic. It was a total waste of a young life, full of potential, even if her current youthful choices were not well-calculated. She was just a kid. The circumstances of her death may be very separate from the circumstances that brought her to the park in the first place. This is also how her parents seem to be choosing to process the loss of their only daughter -- she didn't die at the hand of herself or anyone else, she didn't suffer, and she is gone because of an accident. I can't even begin to imagine what they're going through.
From this outside vantage point of having very few details and having to fill in the blanks with speculation, it seems quite possible that she was there deliberately to complete some sort of mission. She may have parked there for a period of time to wait and/or complete her mission. Where better to park than the parking lot? When her father talks about a U-turn gone wrong, could it be something like this? Green U being what she may have meant to do to leave the parking lot heading SW at first after a possible meet-up (or failed meet-up, or whatever), and the red U being the deadly path she actually chose? A hairpin left turn from the road down the boat launch ramp doesn't make any sense, but a too-wide U-turn out of the parking lot does.