No, please don't say anything more here. I sure hope someone among this "circle of friends" has shared his/her suspicions with LE, however.
I think the meeting was planned. She probably had some idea what time she'd be home, and if the guy showed up early, he just waited in the parking lot knowing she'd be along soon. I wonder if she made any phone calls from the hospital or her father's house. Or from her cell phone, if she had one.
I don't think cell phones were around or ubiquitous for teenagers in 1993. I remember my dad had a huge big big car phone in those days lol. Beepers and pagers were still the norm for anyone in the late 1990s and kids could get kicked out of school because they were also associated with drug dealers. Cell phones started becoming popular ~2000 and I had my first one at 2002. Maybe some in late 1990s but I think 1993 is too early.
Whoever she met was either:
1) a planned meeting ... in which case it should be expected that she was dictating the time to leave the hospital with her family (in order to get back home in time)
2) someone she ran into while picking up carry-out or some other way ... most likely a former friend or boyfriend or acquaintance (as you suggested, maybe even someone she briefly saw in a new light)
3) a neighbor
Maybe she could have got home and called someone from a land-line to make plans ... but that's kind of tight on time whether that could all happen and go get dinner and come back by the time the witnesses gave.