Why does Berthe Erica Crow shriek?

In the book, Berthe Erica Crow shrieks because the lawyer steps on her toes.
The text tells us why Crow shrieks so loudly: in chapter 3, Dr. Jake Wexler cuts out a corn (or thickened callus) from one of her toes. The minor operation leaves Crow's feet in delicate condition.
In chapter 5, we discover that Crow is the cleaning lady at Sunset Towers, the Westing-owned apartment building. Crow is also one of the sixteen heirs in the Westing game. In the chapter, she sits down next to Otis Amber and removes her shoes for comfort.
In chapter 6, the Westing will is read, and the heirs are shocked to discover that they are Westing's "nieces and nephews." According to the will, Westing maintains that he was murdered, and he wants his "heirs" to discover who the guilty party is. This is, in essence, the Westing game.
The young lawyer who reads the will aloud is Edgar Jennings Plum. According to the Westing game rules, each heir will be paired with another. Each pair of heirs will receive $10,000 and a set of clues. The object of the game, of course, is to discover the identity of Sam Westing's murderer, who is presumably one of the "heirs."
Berthe Erica Crow is paired up with Otis Amber (a delivery man). The two are supposed to head to Table Six, so Crow puts her shoes on. Meanwhile, Edgar Jennings Plum is handing out the $10,000 checks to each pair of game participants. During this time, Plum accidentally steps on Crow's sore feet, and this leads her to shriek loudly in pain.