A judge set no bond for Shakayla Denson, who faces a first-degree murder charge.
A witness said they saw Denson exit the Nissan near the intersection of North Rome Avenue and West Aileen Street.
Denson, authorities say, first stole a vehicle from a local auto shop and then drove to the water with her daughter.
Police say it all started at 3:09 p.m. Thursday when Denson stole a Nissan Altima from a auto lot in Tampa.
Chief Brian Dugan held a press conference after Friday's court hearing, but said his detectives are still digging into Denson's background and state of mind leading up to the tragic event. Search and dive teams responded immediately and found the body of a young girl approximately 30 minutes after the initial report. Witnesses were shaken up, the police chief said.
Dugan said the woman is in custody and is being questioned.
Denson is accused of stealing a car from an auto fix shop, then parking the vehicle, walking into the river at about 4 p.m. and leaving her daughter, Je'Hyrah Daniels, in the water.
The child's mother, identified by police as Shakayla Denson, was located by police walking not far from the scene, officials stated. "We're going to have to figure out what her mindset was that took her and put her in a place where she would leave a four-year-old to drown in the Hillsborough River". She is also charged with child abuse and grand theft auto.
They said Denson then walked out of the water and away from the river.
Erica Green is one of several residents at the complex who described Denson's erratic behavior. Je'Hyrah is delivered to Tampa Fire Rescue and rushed to St. Joseph's Hospital. In January 2015, as WTSP reported at the time, Jon Jonchuck Jr., allegedly threw his five-year-old daughter, Phoebe Jonchuck, off a bridge into a river 62 feet below.