The arrest followed after forensic report revealed that the infant was killed by poison, police said.
A case under IPC section 302 (punishment for murder) was registered and the mother arrested from Kundalahalli colony, police said.
Police said the woman admitted to killing the infant by feeding her cactus milk.
She has been remanded to judicial custody for 15 days.
The woman, who already had a daughter, had given birth to another girl on March 4, 2012. The infant died mysteriously on March 12, and the body was buried the same day, sources said.