what does the line dont you be so saucy in speech 14 reveal about the girl

Higgins dismisses the flower girl,

Why, this is the girl I jotted down last night. She's no use: I've got all the records I want of the Lisson Grove lingo; and I'm not going to waste another cylinder on it. [To the girl] Be off with you: I don't want you.

The girl, Liza, stands up for herself, Don't you be so saucy. You ain't heard what I come for yet. She knows enough that these men have come for somethging to do with her lower class. This shows Liza to be spirited even to men of the upper crust.