Altisidora is a fifteen-year-old girl working in the service of the Duke and Duchess, who host Don Quixote and Sancho at their castle in Part 2 of the novel. Altisidora is a prankster who wants in on the fun of messing with Don Quixote. She considers herself to be a very beautiful girl, so she pretends to fall in love with Don Quixote in order to torture his sexual urges. Don Quixote, though, remains steadfast in his devotion to his beloved Dulcinea.
It's only when she finally realizes that the old man won't budge under her fake seductions that Altisidora needs to save her pride, saying, "[H]ast thou the impudence to think that I died for love of thy lantern-jaws? No, no […] for I would not suffer the pain of a flea-bite, much less that of dying, for such a dromedary as thou art" (126.96.36.199). Now, we might not understand all these words (though we're totally into calling old dudes "dromedaries"). But suffice it to say that Altisidora isn't afraid of using some pretty rough language when it comes to defending her wounded pride.
(We've got to hand it to Don Quixote, by the way: silly as he may seem, his devotion to Dulcinea is real, and he endures a lot for it. Most of the men in this book just want to get up a lady's farthingale and leave her in the dust.)
At another point, Altisidora attacks Doña Rodriguez for saying, "she has more vanity than beauty, and less modesty than confidence [and] her breath is so strong, that nobody can endure to stand near her for a moment" (188.8.131.52). It seems like these comments do a pretty good job of summing up Altisidora. While she might look nice from a distance, there are other qualities about her that definitely aren't so nice when you get up close. It's yet another example of the conflict between appearance and reality in the book.