Miss

Yeah but Pinkie probably did her usual thing of skipping around town and telling who ever she saw about camping out for the cider. Dash being Dash was having a nap somewhere, so Pinkie wouldn’t have seen her and wouldn’t have told her.

Well no Pinkie said she wasn't able to sleep last night so she wanted to camp out and told other ponies about it. Those ponies didn't include dash who, by inference, was also sleeping at her home. I would imagine Pinkie to be like "I have to tell Dash about my idea because she loves cider and she's going to be devastated if she doesn't get any because that's what happened last year!" 

As opposed to what you said.  

Or you know there's still the other thing I said about buying some cider for her and giving it to her in line.

Or saving some for her and Fluttershy if they don't get any. 

Or maybe it's just the simple explanation that the episode was just more entertaining due to the the struggle that RD had to go through in order to get cider. Nothing wrong with Pinkie, it's just the writer's decisions. 

And I'm sorry if I seem to always argue about stuff like this. It's not my intention to annoy anyone. I'm just giving my thoughts.