She welcomed her second child (and first with husband Jamie Watson) on Wednesday in Covington, Louisiana, her representative told people.com.
"We are beyond excited to welcome this beautiful baby girl to our family!" Jamie Lynn told people.com.
"Her middle name, Joan, is to honour my Aunt Sandra, who passed away 10 years ago from ovarian cancer. She was the most graceful woman I've ever known," she added.
Jamie Lynn, 27, is already a mother to her nine and a half-year-old daughter Maddie Briann.