Mrs. Younge was originally Georgiana Darcy’s governess in her “establishment” in London and went with her to Ramsgate. It is there that she encourages Georgiana to rekindle her friendship with George Wickham and consent to elope with him.
It is a bit unclear just how scandalous Mrs. Younge is. Darcy writes only that she is a woman “in whose character we were most unhappily deceived”, which may only refer to encouraging the elopement for financial gain. We do know that she is friends with Wickham well before the Ramsgate incident.
After being sacked by the Darcy family, she takes up a “large house” in Edward-street, London “and has since maintained herself by letting lodgings.” Edward Street is south of the Thames and could have been a house of ill-repute, though it is by no means in the red light district. We do know that she puts up Wickham and his underage companion Lydia Bennet later in the novel, suggesting that she’s unscrupulous if nothing else.