Her Wikipedia article is here. She was the daughter of Sophia Dorothea of Hanover and sister of Luise Ulrike and Philippine Charlotte.
From Wikimedia; the veiling reflections exceed my ability to fix them, but her dress is not affected by them.
The round gown is hanging on and the neckline hasn't become completely square in this 1749 portrait. The sleeves are notched with cuffs.
Keywords: Sperling, Friederke Luise von Brandenburg-Ansbach, straight coiffure, hair jewelry, chemise, lace modesty piece, square neckline, three quarter length under-sleves, lace cuffs, bodice, U-neckline, lace bertha, elbow length notched close over-sleeves, lining, cuffs, vee waistline, full skirt, earrings, jeweled bodice, robes