The Wiki article you cite includes some speculation that drifts far away from anything that can be pinned down with the actual, sparse text in question. We can think of the remarkable Beowulf poem as something of a stew that had been cooking for awhile before a scribe put pen to paper. Some morsels were likely around for a long time, but they are so thoroughly "cooked" that it is difficult to assert what they refer to or how the scribe and his audience would have understood them. In other words, even if this part of that part of the poem has roots in a pre-conversion world where powerful female supernatural beings held sway, it does not mean that that this motif is clearly expressed in the poem or that the audience would have nodded in recognition in that direction. There is much we do not know and cannot say with authority because all we can do is speculate about such things. Unfortunately (or fortunately!) the ambiguity is an open door to people asserting all sorts of things as if (we can capitalize that: AS IF) they have authority. Let us understand: they have no firm authority!

Compounding the problem here is the poorly understood term, áglæca. This word appears too infrequently to have good context, and when it is used, its context can seem contradictory since it is a word used to describe both the monsters and the hero. The definitions presented at the end of the Wiki article are reasonable ways to consider the word - that it refers to an awesome, formidable, fearsome opponent, whether hero or monster. When the poet then feminizes the term with the addition of "wif," all we are really able to conclude (as opposed to speculate) is that the intent is something along the lines of describing a "female awesome, formidable, fearsome opponent."

It is tempting to leap from this term - as well as from the vivid description of a formidable female opponent - to imagine that we are allowed a glimpse into a society where people regardless of gender could manifest as formidable warriors (whether with human feet planted on firm soil or in the realm of the supernatural). Recent archaeological evidence of graves of women filled with weapons reinforces this line of thought, so let us leave the door open to exploring the possibilities - and for the wandering of speculation. At the same time, when we walk that path, we must understand the limits of what can be known with firm, fact-based conclusion and how that is different from what we can imagine with speculation.

That complex stew is composed of many intriguing morsels. The "aglæc-wif" is certainly one of them. More than that, however, is Grendel's mother herself - regardless of any vague term used to describe her. She is remarkable, and she may hint at the way the Christian Anglo-Saxon world (and its predecessors) considered the spectrum of possibilities in combat and she may hint at deeper pre-conversion understanding of the supernatural, but all we have are hints.

One may be entranced by speculation about Grendel's mother and her association with Valkyries, et. al., but one must understand that this is speculation not firm conclusion, and it is mighty thin speculation at that!