One reason that Alison's head might be tilted in portraits of her is that Chaucer's Canterbury Tales reveals that the Wife of Bath was deaf in one ear. The injury was actually caused by her fifth husband; he was a clerk and apparently enjoyed reading books more than paying attention to his wife. One night when her husband was reading a story, Alison recalls:
By God, he smote me on the ear, one day,
Because I tore out of his book a leaf,
So that from this my ear is grown quite deaf."
Alison's head-tilt could be a sign of her leaning her head toward her good ear so that she might hear better. She was a sassy and virile woman, so it is also highly possible that the artistic portrayals of her might be trying to catch her vivacious attitude.
In Chaucer's Canterbury Tales, Alison's becomes deaf in one ear. THis happens afte a fight wit her fifth husband. Though she claim to be deaf, she does mention in her illustration of herself in "The Wife of Bath Prologue as birthmarked. Two birth marks to be exact. One one her face and one on her genitial area. These birth marking were of the Goddesses Mars and Venus. Venus on her face and Mars well you get picture. I assume there is a conflict be both of these entities. The Wife of Bath, Alison is a twin personality. She is sexual by Venus yet, controlling by Mars. Perhaps the tilting of the head is showing her lovely side of Venus. Another thing is she is always on the prowl for another (sixth) husband. The fifth husband dies. Alision maybe look to oneside because she is old but she is still sexual aggressive. However, the dominate controlling side of her is still there. In my opinion, Alision has two sides. The one she wants you to see to get the next man, and the one the man will see after she marries him.