Indeed it is Julia Mills, peevish and fine [...] Julia is steeped in money to the throat, and talks and thinks of nothing else. (64.17)
In the last chapter of the novel, David relates that Dora's old friend, Julia Mills, has married an extremely rich man in India. She has loads of servants and fine clothes and so on. But the money has made her "peevish" – no longer contented with anything, but always fretting. The old days when Julia Mills was so generous in bringing David and Dora together are quite gone. Instead, she "talks and thinks of" money and nothing else. The implied message of this book seems to be that only those who work for their money deserve to have it; otherwise, you get careless, selfish characters like Steerforth and Julia Mills.