Can Gullveig of the Nordic Ascendant be used as material for the summon of another Gullveig?
Does this mean the Gulllveig can be used as material for itself?

No it can't.
Link Monsters have no Level nor Rank. From the Wiki on Link Monsters, emphasis mine:

Link Monsters have a Link Rating in place of a Level or Rank. [...]
Link Monsters do not possess Levels or Ranks, therefore they cannot be used as material for a Ritual, Synchro, or Xyz Summon. Also, Level or Rank-modifying cards such as &quot;Harmonic Waves&quot;, &quot;Feedback Warrior&quot;, or &quot;Xiangsheng Magician&quot; do not affect Link Monsters.

As Gullveig specifically asks for a Level 5 or lower monster that means you can't use her as a link material to summon another copy of Gullveig.