While I do think Raintree has some points, I don't think they are as cut and dried as she presented them.
Knowing where you parked your car: If the OP parked in one lot, walked to the friends lodging and then they walked to a different place to dine, I can understand maybe needing help retracing your steps, especially on some college campuses. While I would probably be able to find my car again, if on a time schedule I'm sure I would assume my friend would be able to navigate me back to my car a lot quicker.
Texting before driving off: the OP had a passenger in her car who would be capable of sending a text. I can understand being in a hurry to get started and thinking my passenger would send the text for me while we were on the road.
True. She wasn't familiar with the area and it sounds as though she had no reason to believe that Lucy and Allison wouldn't get moving at the appointed time and walk back with her. Why wouldn't they? It was all agreed upon in advance.
And she had no reason to think Lucy might refuse to send a text. By the time she realized how tight they were cutting it, she had no time to stand there and send a text.
Was Allyson in on the importance of leaving on time? Because I'm wondering why Allyson didn't also jump up to say, "well, let's start walking back" as soon as it became apparent that the OP wanted to get going, NOW. What if the OP had asked Allyson directly to show her where the car was, regardless of what Lucy was doing?
I agree that yes, the OP could have left Lucy stranded. Lucy could still get home; it just would have taken her a LOT longer.