Do I have a right to be upset?

The situation is I do not have a car. Never have nor could I ever afford one. Every weekend I go to the camper but I have absolutely no way back into town. I'm basically trapped out there. Now next weekend is my niece's birthday and I've been told specifically my sister will not be giving me a ride back into town because everyone will be drinking. I called a taxi ride and they said the resort is too far from town and it's inconvenient to come pick me up. I asked a friend as well obviously I would pay him but haven't heard back. I told my sister then I just will not go out to the camper because I have to be home that night to get ready for my next day of work and a flight I have to catch. She said that I have to go to the camper and I would be just fine going in the morning to all my events. I'm upset about it and feel bad but I don't think I will be going to my niece's birthday if I can't find a ride home. That's the story basically. I just needed to vent.
Do I have a right to be upset?
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