Hi B.. My daughter, my oldest at 9 1/2, often has a dark cloud over her head, too. I discussed this issue last yr on another forum and discovered that even at eight, girls can be ovulating w/out menstruating, so yes those "hormones" can be part of the reason.
But what to do, I know. I also have 3yr-old boy/girl twins, and I still hear quite often how she misses those 6yrs of being my only. When they were infants, we took her on hotel getaways for her b-day and such (for a break for me, too!) and now she still thinks she's supposed to get little vacations w/ just her. I explained that her little brother and sister will most likely never get "only child" trips, and I never did as a middle girl! Maybe some of this sinks in as she spends time alone in her room...? Both husband and I spend 1 on 1 time w/ her, but it doesn't take long for us to hear "Aw I don't wanna go if the twins are coming." Now she plays wonderfully well w/ them at home, and can go to the other extreme and play a game w/ them if I need to rest off a migraine...
Recently the kids and I went to play mini golf, and she was actually excited about seeing them "play" for their first time, and she and I planned on keeping score just between us two. But when she saw I actually was GOOD (I told her that's what Dad and I did for dates before marriage and kids) she decided to QUIT b/c she was "bored." Now this was a very fun course.
I'm rambling! I can't figure her out! I pray often for her, and for guidance in raising her. I tell her I love her everyday. I've thought about an "attitude chart" to let her know certain attitudes won't be tolerated (like this miserable look she has at church!) I let her know she can privately write about her feelings, or talk to me or her school counselor when anything causes discontent.
I'm mostly responding to let you know you and your daughter are not alone!
Here's something I'm adding since I've posted my response: Find out where her compassion is (homeless pets, children affected by the war, lonely elderly in nursing homes...) When my daughter and I are out, she often asks to visit this shelter for cats and dogs. We have 2 cats that she loves tremendously, so we all agree no more pets for now, but she just wants to visit them and give them attention and love. Then at night we pray for them to find homes, and it make her feel thankful that we rescued our 2 cats.
And I do see her thinking when we watch on TV the tragedies of war or natural disasters and how children are affected.
K., Ohio