She was the second wife of Prussian King Friedrich Wilhelm III following the heroic Queen Luise who died in 1810. She married the King in secret in 1824, partly because she was Catholic and partly because she was non-royal. She converted in 1826. Her Wikipedia article is here.
Kreuger also shows the waistline sliding down to its natural place in this portrait of Princess Leignitz. Her dress also is shaped instead of draped.