The incident occurred yesterday when the two entered into a dispute over some property related matter after which the accused, in a fit of rage, threw acid on her mother's face, they said.
The victim, who suffered serious burn injuries, has been admitted to a private hospital here.
The accused, who was later detained for questioning, appeared to be in an unstable state of mind during interrogation, DIG Amitabh Yash said, adding that she has been sent for medical examination.
No case has been registered and further investigation into the matter is on, he said.