She's never told anyone, and never plans to... but Clarissa's parents are separated. She went with her dad, and her brother went with her mom. Her dad is absolutely loaded, and has no problem showing that through his daughter... but she feels like she has to make him look good. She has little control of her world - he controls everything - so she feels, at school, like she has to be in charge of everything there on his behalf.
Also, before their parents separated, she had been very close with her brother. Too close, in fact, as they actually had relations a few times.
She recently found out her brother died in a car accident, but his funeral was months ago, and she missed it. This fact has caused her to triple down on her control freak act.