Daughter's Angry Outbursts and Mood Swings

About 2 years ago, when she was 6, my daughter started having these little moments where she'd get frustrated and pretty much blow a gasket.  Ok, we were told that it's her age and she'll eventually outgrow it.  I've half serious/half jokingly told friends and family that she has PMS really badly.  Speed forward 2 years.  Now, her moments of being so very angry have gotten worse and she tends to scream, cry and fall apart over the least little thing.  We just stand back and and make sure she doesn't hurt herself or break things in the room.  My husband works from home so he's able to be there after school and help her with her homework. Yesterday, I came home and he meets me at the door with this very strange look on his face.  I immediately ask what's wrong and then I hear her...screaming, crying and throwing things around in her room.  He said that she got thru her homework ok but when he asked her to do her required 20 minutes of reading she didn't want to do that today.  She normally loves books and has a great imagination but yesterday just wasn't one of those days where reading is fun.  I very calmly go about my normal at home chores, get into comfortable clothes, etc..Then I go into her room where she's down to just crying loudly and proceed to strip her down to her undies.  For the first time since she was a non-crawling infant, I swaddled her up in her sleeping bag in the very same way that you'd do with a baby.  The crying stopped and she just lay there quietly.  Just like that.  I cuddled her up to me and just held on to her.  She might have fallen asleep for a few minutes but not sure about that.  This was a very strange thing and it scared me silly.  We had already planned on having her evaluated for ADHD but thought we had a little longer in which to find doctors and make appointments.  After yesterday, it seems we don't have the time.  I'm having my own eval done on Friday and after mentioning my daughter to the doctor, he said to bring in her in for an "observation only" visit at the same time.  We've known him for years and I trust him to just tell us the truth as to what needs to be done first.  My poor baby.  

Anyone have similar experiences or advice to share?