Final answer:
Demeter searched extensively for Persephone, and upon her return promised bountiful harvests and a better afterlife. Their story is integral to the Eleusinian Mysteries and the Thesmophoria, where Demeter's laughter ends her period of fasting. The texts do not specify Demeter turning nymphs into anything, unlike some other myths.
Step-by-step explanation:
After Demeter discovered that her daughter Persephone was missing, she began a long and arduous search across the earth. In one version of the myth, when Persephone was finally returned to Demeter, Demeter's joy was immense, and she promised fields yellow with corn and a better afterlife.
This reunion and the search for Persephone formed the central narrative of the Eleusinian Mysteries, an ancient Greek festival in honor of Demeter and Persephone, which included various rituals and was marked by a great rejoicing and brandishing of torches, mimicking Demeter's search.
In the myth, Demeter's emotional journey and fasting ended when the old woman Baubo made her laugh, thereby easing her sadness. This part of the myth symbolized the lifting of a ritual fasting during the Thesmophoria, another festival in honor of Demeter, and was associated with mocking and indecent speech symbolizing a return to 'normality' after a period of 'abnormal' behaviour. The connection of Demeter and Persephone's myth to these festivals demonstrates the importance of their story in ancient Greek religious life and the varied expressions of their worship, which sometimes included the transformation of other beings into different forms as part of the associated rituals, though no specific nymph transformation is described within these provided texts.