“I am an only child. I have one sister.”

—Woody Allen

When Stephanie’s mother asks her in Four to Score, “Why can’t you be more like your sister?” (22), surely I’m not the only reader who winced. Poor Stephanie. No woman wants to be compared to her sister. Well, maybe Nicky Hilton does. But I bet the S-word is a sore point with Ashlee Simpson. Sisterhood is a complicated relationship that includes love, jealousy, rivalry, and sometimes even hatred. And it’s probably fair to say that all parents end up making comparisons between their children and often also assigning roles that are hard to shake: good versus naughty, smart versus pretty, tidy versus messy.

“If you don’t understand how a woman could both love her sister dearly and want to wring her neck at the same time, then you were probably an only child.”

—Linda Sunshine

We are first introduced to Stephanie’s “perfect” sister Valerie in the seventh book in the series, Seven Up. To begin with, Stephanie only ever mentions Valerie to bitch about how serene and, by implication, boring she is. “When we were kids Valerie was the perfect daughter. And I was the daughter who stepped in dog poo, sat on gum, and constantly fell off the garage roof in an attempt to fly” (Hard Eight 5). Stephanie, when comparing herself to Valerie, constantly finds herself lacking. At the same time, although she categorizes herself as a mess and Valerie as a  …