I don't remember Muriel being named in the film. During their first conversation, Gretel even asks her what her name is, and she responds that Gretel is unworthy of pronouncing her name. Even -I- feel like that's too much of a technicality anyway, though, and I too would pass the film based on that conversation alone.
One possibly interesting aspect of this film is that, to me at least, violence seems to be played out in a surprisingly egalitarian manner. There is male-on-female violence, female-on-male violence, male-on-male violence, and female-on-female violence, and it's all treated pretty much the same way, without female characters being treated as any weaker or less capable than male characters when it comes to violence.
There are 4 named female characters: Gretel, Muriel the evil witch, Mina the white witch, and Adrianna, the children's mother (seen only in flashback)in addition to several covens' worth of mostly female witches. (Two of them are referred to on IMDB as "Horned Witch" and "Red-Headed Witch", which aren't exactly names, although they definitely play a significant role in the action.) Gretel and Muriel have several conversations and plenty of interaction; although the big plot-twist conversation involves Hansel as well (not surprising, since it reveals their backstory and what happened to their parents), I think there's more than enough discussion/ass-whooping between Gretel alone and Muriel for this to qualify--the main storyline is the relationship between the siblings, and their attempting to save the children by killing as many witches as possible; the Hansel/Mina relationship, such as it is, is very much secondary. (Muriel and Mina also interact near the end, and while technically it involves Hansel, it's not about him as it is Muriel overpowering and killing Mina. Either way, though, Gretel and Muriel together are enough for the movie to pass the test.)