She makes an appearance in the Skáldskaparmál section of the Prose Edda, in the context of Thor's battle with the giant Hrungnir. After Thor had despatched Hrungnir with his hammer Mjollnir, Gróa was asked to help magically remove shards of Hrungnir's whetstone which had become embedded in Thor's head. Unfortunately while Gróa was about her work, Thor distracted her by giving her news of her husband's whereabouts (he had earlier helped Aurvandil cross the river Élivágar), telling her that her husband was now at home. Gróa's spell miscarried and the pieces of whetstone remained permanently embedded in Thor's head.
Gróa is also a witch or völva, summoned from beyond the grave, in the Old Norse poem Grógaldr, (a section of the Svipdagsmál), by her son Svipdagr. In death she has lost none of her prophetic powers, and is able to assist him in a successful conclusion of the task which he has been set by his cruel stepmother.
It is possible that this second Gróa is the same as the first one.