Seriously, she is a fool. I have been to way more shows than i can count. You DO NOT wear fucking high heels, you don't even wear sandals, i hate sandals people let alone high heels. Proper footwear is just one of the rules/etiquette of a show.
Here, i will help her out:
1. Wear shoes if you expect to go near the stage
2. Put your hair up if it is long/big
3. Never wear the shirt of the band you are going to see unless it is so vintage that you picked it up at their first show and it is like 10 years old
4. Even worse than 3, never put on the shirt you just bought of the band you are going to see(unless you are cold from the sweat from the pit, or someoen bled all over your shirt, etc)
fell free to add more, i kind of wanna make a thread on this, curious to see what other rules you guys can come up with
completely irrelevant to all this and just a random 2am thought that i have no idea why i'm posting, but i've been going to shows for 5+ years and decided somewhere along the way that wearing real shoes sucks and have been wearing sandals since and heels if i feel like it (i'm 5 feet tall, they help more than they hurt). obviously if i'm going to pileup to this is hell or something i'll go out of my way to dig up some legit shoes, but it makes me wonder what people like you think when you see me wearing sandals, haha
also, please DO NOT put your [not you since you're a dude, just general you] hair up, that is so fucking annoying. mass of hair floating about >>>> ponytail nub stabbing you in the face.
addendum to #3: it's also legit to wear the shirt of the band you're seeing if you reconstructed it or something like that, something hella awesome though, no lame "cut up the sides and tie them back together" shit. i wouldn't do it anyway but i don't generally think of chicks who do that as douchebags