I too am a member of the 7 year old girl drama club!!! Mine turned 7 in August and I know what you mean. Now, thankfully, it isn't hard to fix. We still deal with drama, but at a very small scale now and when it's worse, we implement the following things.
In the beginning, when she showed me disrespect or exploded over something, I explained to her that I just didn't understand where her bad behavior was coming from, especially since she was such a good girl. So, after thinking long and hard, I decided that she must not be getting enough sleep. This was followed by a "yes I am!". So I said, "well, it's the only reason that really makes sense to me, so I think it would be a good idea to switch your bedtime to 8:00 for awhile instead of 8:30 to see if it helps. After a few days of you being rested up and not having problems with bad behaviors, then we'll go back to your normal bedtime" So, that first time, I think she had her 8:00 bedtime for 5 days if I remember right. On the last day, it had been 2 days of no drama, so I brought up to her that I thought she maybe was rested enough to go to bed at 8:30 again, but if she chose bad behavior the next day, we'd go back to the 8:00 bedtime again. She really hated this, which is why it works!!! Now, if you don't have a bedtime implemented at your house, what a great time to start doing so! The next time she's crappy, tell her you think she needs to be on a schedule from now on (which is absolutely necessary for all kids in my opinion anyway), and tell her you'll start out with 8:00, but if her attitude is good for a couple of days, you may consider making it later.
Another thing, do NOT argue with her, not even a tiny bit! If you say "bring me your hamper please" and she says "but, I'm playing!!!" Ask her, "are you arguing with me?" If she continues, tell her she owes you 15 minutes that night since she's holding you up on your work. If it's something else, like say she said she wanted pop tarts for breakfast, but then after you give them to her she says she wants something else, don't get involved in her dialogue about it. Instead say "I'm not going to argue about it...eat!" If she gets sassy, tell her to go to her room andwhen she's finished, she can come back out. I constantly am saying "do you need to take a break?" Or if her behavior's worse, I just say "go to your room until you're finished" Almost everytime, I get a "I'm done", but I just say "I said go to your room" If she says she's done again, I just point to her room, I usually don't even look at her after the initial telling her. You have to remember that kids will only do what they're allowed to get away with. If you decide to NOT put up with something, and enforce specific consequences, the behavior WILL stop. Sometimes, it's just tricky to find what works, but don't give up! If you have specific situations that you're wanting some advice on, post them in your "what happened" and I'll check back.