The goddess is the symbol of the land, whose union with the prospective king ensures his sovereignty. Without union with her he cannot become a king acceptable to his people. Without her rightful ruler she is old, old and occasionally deranged. When united with her sovereign she frequently changes from her former shape of an ugly woman to a beautiful young girl.
The best known example of this metamorphosis occurs in “Echtra Mac nEchach” (The Adventure of the sons of Eochaid). Eochaid is the prehistoric king whose son is the legendary saga figure Niall Noigiallach…
While hunting in the woods, Niall and his brothers try to get water from a well, guarded by a hideous old hag. She demands a kiss in exchange for the water, and all deny it except Niall. He embraces her, whereupon she becomes a beautiful young girl.
“”And who are thou?” he (Niall) pursued.
“Royal Rule am I” she answered.”
Muireann Ni Bhrolchain, Women in Early Irish Myths and Sagas