Rollercoaster
Her moods are like a rollercoaster. Only it's worse because she can't see the track ahead. The dips and dives come up out of nowhere. They scare her. And sometimes a great big hill will come, and her mood will soar. But it's not like she can enjoy it, because half of her is still back down at the bottom of that hill. Then, before the effects of that bottom can wear off, before she can enjoy the heights she's at, she's back down again.
Stupid rollercoaster.