The teenager qualified for the 16-year-old 50m and 100m backstroke, as she went in the 50m event first, producing a staggering 31.76secs in the heat, just outside her PB, giving her 10th place.
The time was enough to reach the final in the evening where Ellie produced a superb 31.73secs, ensuring a fantastic eighth place overall.
King then went in the 100m event, and produced a brilliant 1.08.9mins ensuring 12th place which was only narrowly away from another final as she put in another great account at her second nationals.
Mum Christine King said: “Ellie has loved the water since she was a baby and we wanted her to learn to swim to be safe in and around water.
“This developed when she joined Dunstable Swimming Club at 11 where she found a love for competitive swimming.
“It can be hard to fit in Ellie’s training schedule, which is often twice a day, and competitions over many weekends, with a balanced work and home life but Ellie works hard to achieve her goals.
“Seeing her reach competition at a National level makes us very proud and makes all the early mornings and late nights worthwhile.
“Her interest in the sport has already shaped her future in many ways and having completed her GCSEs this summer she plans to study sports at Dunstable College and continue on to university to take this further, having already begun working part time as a swim teacher.
“We are very proud of Ellie’s achievements but we really want to thank the staff and volunteers and the many families of Dunstable Swimming Club who have supported her all the way.”
Tim Hutton, head coach of DSC, added: “It was an awesome performance from Ellie and great achievement to be able to balance swimming training and GCSE year.
“Ellie has done herself, her family, the club and the town very proud.
“From next week the hard work starts for DSC to lay good foundations for the new season.”