Blackmailing is sometimes, something that smart children do, the problem is that they use their intelligence in a bad way. I'm sure she is a good dancer, if she's addicted to the point she wants to dance at night it means she really likes it...

Haha, it's funny because when I was a child I had tantrums too because I wasn't allowed to use the computer for a long time. And here I am today, spending hours in front of the screen of my computer, lol.

Personally, I think the best punishment for her is to work for what she wants. I mean, for example, she's allowed to dance as long as she does the washing up, or clean her room. I think this can be motivating for her and at the end of the day she will end up very tired before the night starts.

Also when my little cousin (which is very mischievous and bad behaved) coma to my house before I moved, I put him to draw something very difficult or construct something great with his building bricks, I told him "I don't think you can do it" and he felt challenged and spent hours making that drawing until I said it's good, haha.

Well, don't take these advises too seriously, I'm not a parent yet, but they can work sometimes. It's nice that you don't hit your children, most parents do that and get not other results than fear and it's very popular here in my country (what a casualty one of the top countries with highest crime rates in the world).

Warm greetings and good luck with you child!