Original: Catherine gave birth to her only child - a daughter, Mary Seymour - on 30 August 1548, but Catherine died only six days later, on 5 September 1548, at Sudeley Castle in Gloucestershire, from what is thought to be puerperal fever or puerperal sepsis, also called childbed fever.
Simplified: She gave birth to their daughter, Mary, at Sudeley Castle on 30 August, 1548, but she did not recover from the birth and died soon afterwards on 5 September, 1548.