There is just a possibility that Lord Craven's mistress,

…now living with him at Ashdown Park.

may have been a very famous "lady" indeed.

At this time, by my calculations, Lord Craven , that is William Craven (1770-1812) 7th Baron and from 1801 1st Earl of the 2nd creation, of Hampstead Marshall and Ashdown Park, Berks ,was involved with a very famous courtesan, Harriette Wilson.

She does not mention living with him at Ashdown Park in her memoirs( famously published after attempts, some successful , to blackmail her former famous lovers, whose secrets she was about to reveal) but what she does say about him is rather cutting and dismissive:

I shall not say why and how I became, at the age of fifteen, the mistress of the Earl of Craven. Whether it was love, or the severity of my father, the depravity of my own heart, or the winning arts of the noble Lord, which induced me to leave my paternal roof and place myself under his protection, does not now much signify: or if it does, I am not in the humour to gratify curiosity in this matter.

I resided on the Marine Parade, at Brighton; and I remember that Lord Craven used to draw cocoa trees, and his fellows, as he called them, on the best vellum paper, for my amusement. Here stood the enemy, he would say; and here, my love, are my fellows: there the cocoa trees, etc. It was, in fact, a dead bore. All these cocoa trees and fellows, at past eleven o'clock at night, could have no peculiar interest for a child like myself; so lately in the habit of retiring early to rest. One night, I recollect, I fell asleep; and, as I often dream, I said, yawning, and half awake, "Oh, Lord! oh, Lord! Craven has got me into the West Indies again." In short, I soon found that I had made a bad speculation by going from my father to Lord Craven. I was even more afraid of the latter than I had been of the former; not that there was any particular harm in the man, beyond his cocoa trees; but we never suited nor understood each other.
See:The Memoirs of Harriette WilsonWritten by Herself,Volume 1,Chapter 1, Page 5.

Harriette was born on 22nd February 1786: she would have been 15 years old in 1801 . So it just might have been her, residing in immoral splendour at Ashdown Park.

Lord Craven of course knew much about cocoa trees , I shoud imagine ,as he had had first hand experience of them. He had visited the West Indies: he had asked Tom Fowle, Cassandra's fiancé to accompany him , when as Colonel to the 3rd Foot Regiment- The Buffs- he was sent to the islands as part of the convoy commanded by Admiral Hugh Christian escorting General Sir Ralph Abercromby's 19,00 strong force to subdue French interference in the islands.

Tom Fowle accompanied him as his private chaplain on that ill-fated voyage to the West Indies in 1795 but of course did not return, and Lord Craven was reported to have said that had he known of Tom's engagment to Casandra he would not have allowed him to go to the West Indies on account of the dangerous nature of the climate.(see page 91 and 101 : Le Faye : A Family Record,

Poor Lord Craven was obviously explaining to the bored Harriette of his battles on the islands….she , a little like Lydia in P+P IMHO,, seems only to have heard and understood one word in ten.

Lord Carven appears to have had a "thing" for women of a certain classs:

Here's a link to Ashdown Park, now a National Trust property, which is one of the most stunning houses in England, IMHO. Harriette may have been bored there , but at least she was bored in a wonderful setting. ;-)

She wasn’t bored for long: she soon ran away from Lord Cravens delights and cocoa trees to the protection of Frederick Lamb (1782-1853), later 3rd Viscount Melbourne.

And happily Lord Carven eventually found his soul-mate:

In 1805 Lord Craven saw Louisa Brunton (?1785-186o), daughter of John Brunton (a greengrocer turned actor and theatre manager in Norwich), and now making a name for herself as a Shakespearean actress at Drury Lane-her principal parts included Celia in As You Like It, Anne Boleyn in Henry VIII, and Lady Anne in Richard III.

In 1807 Mrs Calvert watched her perform in Brighton, and commented in her diary: 'She is certainly a very handsome woman, but I don't think her looks pleasing. She has prodigious fine black eyes, but she rolls them about too much. Lord Craven is supposed to be very much in love with her, and many think he will marry her.'

Fanny Kemble's mother remembered Louisa Brunton as 'a very eccentric as well as attractive and charming woman, who contrived, too, to be a very charming actress, in spite of a prosaical dislike to her business, which used to take the peculiar and rather alarming turn of suddenly, in the midst of a scene, saying aside to her fellow-actors, "What nonsense all this is! Suppose we don't go on with it." This singular expostulation my mother said she always expected to see followed up by the sudden exit of her lively companion, in the middle of her part. Miss Brunton, however, had self-command enough to go on acting till she became Countess of Craven, and left off the nonsense of the stage for the earnestness of high life.'. . .

'Miss Brunton, at the beginning of December 1807, with characteristic modesty, made her final curtsey on the stage'- and married Lord Craven in December his town house in London.

Later gossip-writers recalled her as 'tall and commanding and of the most perfect symmetry, and her face the perfection of sweetness and expression'.

In 1816 the Countess admired Emma very much, but did not think it equal to P&P.