Page numbers of each edition may not exactly correspond, but it is easy to find the parts you are looking for if you know the volume and chapter numbers.
Elizabeth first meets Lady Catherine de Bourge when she travels to Kent with Sir Lucas and his younger daughter Maria in order to see her dear friend Charlotte Lucas soon after her marriage to Mr. Collins. Elizabeth arrives at Huntsford in Kent with the Lucases in Volume II, Chapter 28. It is in Chapter 29 that the Collinses, the Lucases, and Elizabeth are invited to first dine at Rosings and meet Lady Catherine. It is in this chapter that Lady Catherine firsts enters into conversation with Elizabeth, expressing shock to learn that all five of the Bennet daughters are out in society at once, even before the eldest sisters are married. Lady Catherine also criticizes Elizabeth's lack of education, particularly her lack of education by a governess and also criticizes her ability to express her opinion so forthrightly, as we see when Lady Catherine says, "Upon my word ... you give your opinion very decidedly for so young a person" (Vol. II, Ch. 29).
We learn that Lydia has run away with Wickham later on in the next volume. Lydia has been granted permission to go to Brighton with Colonel Forster and his wife by the end of Volume II, Chapter 41. After that, in Chapter 42, Elizabeth leaves with her aunt and uncle Gardiner to take a tour of Northern England for their summer holiday. They travel as far as Derbyshire, especially to Lampton where Mrs. Gardiner grew up, and decide to take a tour of Pemberley. It is in Volume III, Chapter 43, that they tour Pemberley and run into Mr. Darcy who invites them to meet his sister. After dining at Pemberley, Elizabeth receives letters from Jane detailing the news of Lydia's flight with Wickham. Mr. Darcy comes to the inn to call on Elizabeth while she is reading her letters and shows her a great deal of compassion, saying, "I am grieved, indeed ... grieved--shocked" (Vol. III, Ch. 46). Immediately after, Elizabeth and the Gardiners leave to return to Longbourn.