Why would it be taken that seriously? Take a look at the abstract:
This historical novella charts the events as they unfold within Beowulf through the eyes of the minor character Wealhtheow, Hrothgar’s Helming Queen. The novella tries to remain as historically accurate to the culture of fifth and sixth century Scandinavia, for this is when most scholars agree the historical events of Beowulf unfolded. This fictional account of the Beowulf-poem presents the story within a different genre in hopes of creating an environment that is vivid and more easily accessible to modern readers, especially young adult readers, not only referencing Scandinavian culture but also the role of Anglo-Saxon women.
Introduction: My goal in writing this fictional novella is twofold: to make Beowulf more accessible to modern readers and to expound upon the less articulated female point of view in the poem.
Maybe it can't be called fan fiction if the author is not really a fan of the original epic poem? She probably is, though.