In her wonderful essay, "The Social Centrality of Women in Beowulf: A New Context," Dorothy Carr Porter says the six women in the epic can be divided into pairs according to roles: Wealtheow and Hygd are "queen/hostesses"; Hideburh and Freawaru are (failed) "peaceweavers"; and Grendel's mother and Thryth are "monsters."
I think we all know what queens/hostesses and monsters are, but "peaceweaver" needs explanation:
"Peaceweaver" is a term in modern scholarship reserved for a woman married into one group from another, in an attempt to weave peace among them. As peaceweavers, these women have the potential to hold influence in both groups - potential which does not come to fruition ...
She goes on to say that the monstrous pair of Grendel's mother and Thryth are foils of the others: they are "hostile hostesses and strife-weavers."
I think the focus has to be on Grendel's mother. She is clearly not like the other women. If fact, she's like no other monster. In Grendel, John Gardner presents Grendel's mother as a fat mute, while the filmmakers of Beowulf make her out to be a slithery vixen. I rather like both interpretations, as I do most revisionist portrayals, because it shows an intertextuality that coincides with the times. In other words, our vision of the women in Beowulf may change based on our vision of women today.