Miranda's new behavior

Miranda has been doing a strange thing lately.  She is doing it right now which is why I am thinking about it.  It happens in different ways, but today it was like this:

I picked her up from Sewing class and all was well.  She was in a good mood and told me about the fun things she did that day.  She had a cookie and a hershey kiss that her sewing teacher gave her.

We went to get Parker at swim team practice and she and Elizabeth played in the playground while he finished. She was in a good mood and when it was time to go, she happily went to the car.

We got home. At the door we discussed what each kid had to do. She had to finish her birthday thank you cards. She had three left to do. (Elizabeth finished hers a while ago.)  She was in a good mood still.

Then she started to lose it. She didn't know where her stuff was. I reminded her it was in her card case that Ebba gave her. She had no idea where that was. I told her to look in her room. She went upstairs where she screamed and cried for about 10 minutes yelling things like "I have no idea where this case is!".

Then she walked downstairs with it.  She was still crying.  She immediately started crying more and whining that she didn't know what to do (despite the fact that she had done 17 already.)  I reminded her about how I wrote out all the presents by the kids' name and I wrote out how to write "thank you for the..."  She still claimed she had no idea what was going on and was screaming at this point. So I told her to go to her room until she was ready to be calm. She went upstairs screaming, "I want to throw this book at you! I hate you so much!  I'm so angry right now! You are the worst mom ever!"

Then about 20 minutes later, she came down stairs and said in a very cheerful voice, "I'm ready to finish the cards now."  I said fine and she happily did the card for Amber. No issues or problems at all.

Then we had dinner.  At dinner, Michael said he would take kids bike riding after dinner.  Then something pissed her off and she started being really rude and mean to Michael. Miranda spit (raspberry) at Michael. Several times. Despite warnings to stop.  She returned to her cards and Michael went over to tell her that she would not be going with the other kids because of her behavior.  She listened to him carefully and then when he was done, she started screaming again. I again asked her to go to her room until she was ready to be calm.  She went upstairs where the insults started again. She said "She hated everyone in the family! She didn't want to live here anymore!  Everything was unfair. Etc, etc, etc."  She watched the kids go off with Michael and banged on the window.

Then about 20 minutes later, she came downstairs and said she was ready to finish the cards.  (She also asked if she could watch TV afterwards, which I said No to.)

She is now happily writing another card as if nothing had happened.

Very similar situations have happened many times lately and it concerns me greatly.