I am reading a Norton Critical Edition this time and this very speech is addressed with a note.
R.W. Chapman has emended this passage to give this line to Mr. Bennet, for reasons Mr. Chpaman advances most persuasively "When is your next ball to be, Lizzy?" is given to Kitty by all editions. But why should Kitty ask what she must have known? And why should she call it 'your ball'? The speech is of couse Mr. Bennet's. In A [the first edition of 1813] it begins a line, and the printer merely failed to indent the first word." , Oxford edition, II, 391.