Andrea Rodriguez told police she and the grandmother forgot the 26-day-old child while they shopped at a local Market Street.
According to police, the infant was left in the car on an 88 degree day with the windows up and the doors unlocked.
Rodriguez did not respond to pages over Market Street's intercoms.
Police say they finally found Rodriguez in the check-out line.
Rodriguez is currently behind bars for abandoning/endangerment of a child and several other misdemeanor warrants from unrelated incidents.
The child is in stable condition.