We had a little incident at a playdate recently.  We met another family at the park for lunch. My daughter doesn't know the little girl all that well, but she had a lot of fun on the playground with her. We went on to ride the train at the park and she said she wanted to sit alone (vs with her friend). I said, “oh honey, let's sit with our new friend” and she said no.  There were limited seats so the other mom sat with her daughter and son in the front row seat (it was a quick shuffle). My daughter had a fit because she wanted to sit in the front and kept saying "no one is listening to me." She and I ended up sitting together a few seats away from them and she kept saying "they are so mean, they are so stupid, I am never playing with them again, I just want to scream so badly."
Should I have just taken her home right after the train ride? 
Why does she get particularly stuck around the “no one is listening to me” scenarios?