I found a print of Lady Anne and started dig. This minor aristocrate was very well documented by the portraitists of the day, especially Richard Cosway.
According to her her Wikipedia article, "...Anne Conway was born in Sevenoaks into an aristocratic Whig family; she was the only daughter of Field-Marshal Henry Seymour Conway (1721–1795) and his wife Caroline Bruce, born Campbell, Lady Ailesbury (1721–1803), and was brought up at the family home at Park Place, Remenham, Berkshire.
In 1767 she married John Damer, the son of Lord Milton, later the 1st Earl of Dorchester. The couple received an income of £5,000 from Lord Milton, and were left large fortunes by Milton and Henry Conway. They separated after seven years, and he committed suicide in 1776, leaving considerable debts. Her artistic career developed during her widowhood..."
The Duchess of Devonshire's Gossip Guide to the 18th Century has an excellent article about her here.