How to handle talking to someone who potentially ditched you at a hang out?

I've had some life events that have knocked my sense of fair expectations of how we all should treat one another, so want your help. Thanks!

I have a college class mate (I'm a guy), she invited me to go to a music festival with her friends. Cool.

We all meet up. And then I say "hey I'll be back, I'm going to go check out this other performer at the other stage I like for a little bit. She says "Cool, I'll be right here, and I'll let you know if we go elsewhere." KEep in mind she's not drunk or doing drugs. And phone signals were working.

So I leave for 40 minutes. I go back to the other stage and can't find them. I text and ask where they went. I text again 20 minutes later along with a funny joke. She doesn't replyl 3-4 hours later and says "lol we are just leaving now! it was a fun concert!"

1. Do I assume the best and she just kind of forgot to text back and say "Wish you texted back! haha. Wanted to rejoin you all!"
2. Do I go in hard and say "That was not cool. I told you I'd come back and we were in a group and you said you'd text me if you all moved." This seems like it's a little shaming.
3. Do I say "It feels like you ditched me the other day." That's a little light but still kind of shares how I feel about the situation that I'm kind of upset, unlike option one.
4. Straightforward to the point with "Hey did you ditch me?"
5. And do I ask for an apology?

Probably won't see this person in college again. But I'm uncomfortable not saying anything beacuse I feel so undignified and stomped on if I don't.