There is no exhausting the sources that may have shaped Goblin Market. I've just been reading Mary Cowden Clarke's The Girlhood of Shakespeare's Heroines published in three vols 1850-52 in which she created prequels for fifteen female characters.
I am struck by a parallel between Christina Rossetti's tale of Laura and Lizzie with that of Cowden Clarke's Ophelia and her rustic companion Jutha. [ Ophelia, as you did not know, was fostered with a peasant family while her parents served as Danish ambassador and wife in Paris.] Daily Jutha and Ophelia wander the fields and woods, until they meet a fine nobleman out riding, who dallies with and seduces Jutha; pregnant, she then pines and dies.
It's only a fore-echo of Goblin Market, but one can imagine Christina reading Clarke's book to the girls she taught in Frome and at Highgate Penitentiary, and then 'borrowing' some of its elements when her poem about temptation and seduction was conceived around 1858-9.