Blokova’s fingers were cut off by the Nazis as punishment for prisoner escapes.
The Blokova has only three fingers. She is the leader of the prisoners, but she is a prisoner herself. She lost the other two fingers when prisoners attempted to escape or rioted.
“…If she loses control of her zugangi, she will be a two-fingered whatever –you-cal- her,” said Rivka, smiling …. (p. 137)
Blokova does lose the third finger, when Shmuel and Yitzchak try to escape. They are not successful, but she still has to be punished to set an example.
The Nazis were able to control the prisoners by getting other prisoners to control them for them. It is much easier to punish one person when things go wrong than to try to control all of the prisoners.
She lost them because she didn't take care of the people she was in charge of.