If you thought "Wow, crows are pretty much the most ominous bird around," or "Yikes. Crows are pretty much always symbols of death," don't worry—you're not alone. Poor Berthe's last name scares the majority of the characters in The Westing Game, leading them to think that she's the murderer.
But she's more of a red herring than a black bird.
Crow—everybody just calls her by her last name—is the mysterious cleaning lady at Sunset Towers. She seems to hide in plain sight:
How come he didn't know that? Because no one ever wonders where a cleaning woman lives, that's why. But he wasn't like that, was he? (18.23)
We know she's also a recovering alcoholic, and she seems to be in some kind of relationship with Otis Amber. She gets agitated pretty easily, and she seems to have a special fondness for Angela, who she thinks of as a blonde angel. As her partner in the game, Otis is pretty upset when Crow loses their clues, but we find out later that Crow didn't lose them... she gave them away.
The fact that all the clues seem to be leading to Mrs. Westing—and the idea that Mrs. Westing is hidden among the heirs—is confirmed when the missing words from everybody's clues spell out Crow's full name. But it's all a classic case of misdirection. The clues have little to do with the answer to the real mystery hidden in the will: "find the fourth."
Crow's not the fourth, and she's not the answer. The game the will sets up just isn't that easy. So why does it draw so much attention to her? Maybe it's to test how smart the heirs really are. The judge is worried the game is set up for Westing to get revenge on his ex-wife, but we find out later that's just not true—Westing's been looking out for her, in a way, all along.
All signs also point to the fact that Crow, like Flora, is a grieving mother. In retrospect, we can see how her daughter Violet Westing's death permanently broke her. She turns to alcohol, then religion, and we find out she abandoned her husband and what was left of their family. In the end, though, she finds happiness with Otis.