Gudmund's answer begins:
Fadir varattu
fenrisulfa....
The evil woman with whom one of the two heroes compares the other is said to be a vala, who has practised her art partly on Varin's Isle partly in Asgard at Alfather's, and there she was the cause of a war in which all the warriors of Asgard took part. This refers to the war between the Asas and Vans. It is the second feud among the powers of Asgard.
The vala must therefore be Gulveig-Heid of the myth, on whose account the war between the Asas and Vans broke out, according to Völuspa. Now it is said of her in the lines above quoted, that she gave birth to wolves, and that these wolves were "fenrisulfar." Of Angerboda we already know that she is the mother of the real Fenris-wolf, and that she, in the Ironwood, produces other wolves which are called by Fenrer's name (Fenris kindir—Völuspa). Thus the identity of Gulveig-Heid and Angerboda is still further established by the fact that both the one and the other is called the mother of the Fenris family.
The passage quoted is not the only one which has preserved the memory of Gulveig-Heid as mother of the were-wolves. Volsungasaga (c. ii. 8) relates that a giantess, Hrímnir's daughter, first dwelt in Asgard as the maid-servant of Frigg, then on earth, and that she, during her sojourn on earth, became the wife of a king, and with him the mother and grandmother of were-wolves, who infested the woods and murdered men. The fantastic and horrible saga about these were-wolves has, in Christian times and by Christian authors been connected with the poems about Helge Hundingsbane and Sigurd Fafnersbane. The circumstance that the giantess in question first dwelt in Asgard and thereupon in Midgard, indicates that she is identical with Gulveig-Heid, and this identity is confirmed by the statement that she is a daughter of the giant Hrímnir.
The myth, as it has come down to our days, knows only one daughter of this giant, and she is the same as Gulveig-Heid. Hyndluljod states that Heidr is Hrímnir's daughter, and mentions no sister of hers, but, on the other hand, a brother Hrossthiofr (Heidr ok Hrorsthiofr Hrimnis kindar—Hyndl., 30). In allusion to the cremation of Gulveig-Heid fire is called in Thorsdrapa Hrimnis drósar lyptisylgr, "the lifting drink of Hrimner's daughter," the drink which Heid lifted up on spears had to drink. Nowhere is any other daughter of Hrimner mentioned. And while it is stated in the above-cited strophe that the giantess who caused the war in Asgard and became the mother of fenris-wolves was a vala on Varin's Isle (vaulva i Varinseyio), a comparison of Helgakv. Hund., i. 26, with Volsungasaga, c. 2, shows that Varin's Isle and Varin's Fjord were located in that very country, where Hrimner's daughter was supposed to have been for some time the wife of a king and to have given birth to were-wolves.
Thus we have found that the three characteristic points—
unsuccessful cremation of an evil giantess,
her regeneration after the cremation,
the same woman as mother of the Fenrer race—
are common to Gulveig-Heid and Angerboda.
Their identity is apparent from various other circumstances, but may be regarded as completely demonstrated by the proofs given. Gulveig's activity in antiquity as the founder of the diabolical magic art, as one who awakens man's evil passions and produces strife in Asgard itself, has its complement in Angerboda's activity as the mother and nourisher of that class of beings in whose members witchcraft, thirst for blood, and hatred of the gods are personified. The activity of the evil principle has, in the great epic of the myth, formed a continuity spanning all ages, and this continuous thread of evil is twisted from the treacherous deeds of Gulveig and Loke, the feminine and the masculine representatives of the evil principle. Both appear at the dawn of mankind: Loke has already at the beginning of time secured access to Alfather (Lokasenna, 9), and Gulveig deceives the sons of men already in the time of Heimdal's son Borgar. Loke entices Idun from the secure grounds of Asgard, and treacherously delivers her to the powers of frost; Gulveig, as we shall see, plays Freyja into the hands of the giants. Loke plans enmity between the gods and the forces of nature, which hitherto had been friendly, and which have their personal representatives in Ivalde's sons; Gulveig causes the war between the Asas and Vans. The interference of both is interrupted at the close of the mythic age, when Loke is chained, and Gulveig, in the guise of Angerboda, is an exile in the Ironwood. Before this they have for a time been blended, so to speak, into a single being, in which the feminine assuming masculineness, and the masculine effeminated, bear to the world an offspring of foes to the gods and to creation. Both finally act their parts in the destruction of the world. Before that crisis comes Angerboda has fostered that host of "sons of world-ruin" which Loke is to lead to battle, and a magic sword which she has kept in the Ironwood is given to Surt, in whose hand it is to be the death of Frey, the lord of harvests (see Nos. 89, 98, 101, 103).