Elizabeth knows she shouldn't ask about what is going between Wickham and Darcy, but once Wickham opens the door, she is positively avid in her desire to pump him for more information on the Dastardly Darcy.

• what she chiefly wished to hear she could not hope to be told -- the history of his acquaintance with Mr. Darcy.
  
• …said Elizabeth; and then, unwilling to let the subject drop, added…
  
• Elizabeth found the interest of the subject increase, and listened with all her heart; but the delicacy of it prevented farther inquiry.
  
• After a few minutes reflection, however, she continued…
  
• Elizabeth was again deep in thought, and after a time exclaimed,…
  
• After many pauses and many trials of other subjects, Elizabeth could not help reverting once more to the first,… (ch 16)

I hadn't thought Elizabeth such a gossip, or is it simply the subject matter - and the very obliging speaker - that fascinates her?

Elizabeth went away with her head full of him. She could think of nothing but of Mr. Wickham, and of what he had told her, all the way home;