We first meet the loathly lady (also know as the hag) when the knight comes across her in a field on his way back to King Arthur's court. She's ugly, and we're told that "a fouler wight ther may no man devyse" (1005). She's also old and lowborn, which the knight explicitly tells her on their wedding night. All of these characteristics make her a less-than-ideal marriage partner for the knight who, were this another romance, would probably hook up with a beautiful, young maiden. The loathly lady knows this, which is why she's very careful to repeat the knight's promise to her before all the court, in effect forcing him to fulfill her request to marry her. This reveals that the loathly lady is strategic and shrewd when it comes to getting what she wants.
She's also rhetorically skillful, a characteristic that becomes clear in her long speech to her husband on the source of gentility and the advantages of poverty and old age. In this, just as in her strategic cunning, the loathly lady resembles the Wife of Bath herself, if not in the sentiments she expresses, at least with the skill (and lengthiness!) with which she does so. Not only that, but some of her biographical details resemble the Wife's: she's a older woman who jumps at the opportunity to marry a younger man, and she lectures him (some might say gives him a brow-beating) when he berates her for who she is. This is a like how the Wife of Bath treats her young husband Jankyn. These similarities have led some people to conclude that the loathly lady is the Wife's alter-ego in the tale, the character she uses a sort of stand-in to express her point of view.
We can't push the alter-ego thing too far, however; after all, we know from her Prologue that the Wife of Bath certainly isn't about to live a life of poverty. The Wife, moreover, would never yield power back to her husband after he's given it to her. In fact, after the loathly lady transforms into a beautiful young woman, she seems to lose some of her chutzpah, becoming a wife who's obedient to her husband in everything. At this point it's no longer possible to say that she channels the Wife of Bath's perspective. Instead, in keeping with the shift in power at the end of the tale from women back to men, it's like the loath lady channels all of men's fantasies and desires. With the loss of the loathly lady, then, we lose the voice of female power in the tale, which speaks to the lady's role as a symbol of women's sovereignty.