Officers responded Wednesday to a condominium complex in Grover Beach on the Central Coast following reports of an assault on a young girl.
Investigators determined the child was approached by Julie Wilhelmina Rodenhuis and sprayed with a weed killer. The child was treated at the scene and taken to a hospital.
Police Cmdr. John Peters tells the San Luis Obispo Tribune that the girl is expected to make a full recovery.
Rodenhuis was arrested on suspicion of assault with a deadly weapon, battery with serious injury and child endangerment.
Investigators are looking into a motive.
As of Saturday, Rodenhuis remained jailed in lieu of $100,000 bail.
It wasn't immediately known if she has a lawyer.