Friedrich Jakob Hill - So-called portrait of Princess Louise of Nassau-Usingen - Royal Collection

Portrait of Princess Luise Henriette of Nassau-Usingen (1763-1845), but is probably a depiction of her maternal cousin Landgravine Augusta Wilhelmina of Hesse-Darmstadt (1765-1796).
Identification proposed by user Ecummenic (talk) based on the comparison with some portraits of princess Augusta Wilhelmina (see images below)