It's hard to feel sorry for Bibi Haldar at first. Yeah, she's in a terrible state so we're supposed to sympathize with her. She's got some kind of epileptic-seizure illness that's apparently incurable, and her remaining family members—her cousin Haldar and his pregnant wife—aren't exactly loving. She's dirt-poor and not exactly pretty.
But she can be really annoying. Her voice is "louder than necessary, as if she were speaking to a deaf person" (TBH 4). And she talks all the time, especially about getting a man: "Each day she unloaded her countless privations upon us, until it became unendurably apparent that Bibi wanted a man" (TBH 5).
Bibi does change, though. First, she's kicked out of Haldar's house and to the storage room because his wife doesn't want her to "infect" the newborn with her illness. Then, Haldar abandons her completely because he moves away. All of that drives Bibi "into a deep and prolonged silence" (TBH 41), a silence she never fully recovers from since—not long after—a rapist impregnates her.
You'd think becoming pregnant through rape would make the already not-so-stable Bibi go insane or retreat completely from society. Instead, she turns into a practical, resourceful (she takes over Haldar's empty store), committed, working single mother. In other words, Bibi's character is full of surprises.