The Prioress is trying to be very well, dainty. She has all these funny habits, like singing through her nose, speaking incorrect French, and eating so carefully that she never spills a drop. When she sees a mouse caught in a trap, she weeps, perhaps believing that this is how a damsel of the court would behave. Of course, two lines later, we learn that she has no problem feeding her hounds flesh, so her weeping over the trapped mouse is probably, like most of her habits, an affectation – a behavior the Prioress adopts to seem a certain way (in this case, like a courtly damsel), but which doesn't really reveal her true feelings.
Though the Prioress may try to seem dainty, in point of fact she's a very large woman: Chaucer tells us her forehead is a full hand-span broad and, come to think of it, she's not underfed. In keeping with her goal of seeming courtly, the Prioress is very elegantly dressed, with a string of coral beads attached to a pendant that reads "Amor Vincit Omnia," or "Love Conquers All." The beads and the pendant are interesting because this being a prioress, or nun who is in charge of a convent, we would expect her to be carrying rosary beads with a crucifix on the end. But instead she is carrying vanity beads. The pendant, which could refer to God's love, in her case more probably refers to the courtly love between a damsel and hero in one of the romances that were popular reading material for women of this time period.
So here's the thing about the Prioress: as a religious figure, she should be all kinds of things that she very clearly is not. What are these things? Well, take a look at the Parson's portrait, which represents an ideal religious figure in the General Prologue, to find out the answer. With the Prioress, our first example of someone from the religious life, we have not only our first supposedly pious person with her priorities out of whack (a situation we'll definitely see again), but also our first example of someone who's trying way too hard to be perceived a certain way, and how ridiculous that looks.
We should note that the Prioress has a nun with her who serves as her "chapelyne" or secretary, and three priests, who probably help her out by saying mass and administering the sacraments in the abbey she runs. Although we get no portraits of these pilgrims, two of them, the Second Nun, and the Nun's Priest, tell tales later on.