Slug Club, if you're not familiar with or have forgotten the term, is a members-only organization only available to Professor Slughorn's favorite students. Harry was invited once but got himself kicked out when he attempted to access one of the professor's memories. Had he stayed, he may have gotten to know Olivia Jewson's nameless character.
2014 was the best year of Jewson's acting life to date, picking up five roles, but she's only managed another five in the years that have come since. Her Instagram account suggests that might not be accurate though; she's posted several recent pictures of herself on stage, where she's been appearing in Rigoletto at the prestigious Royal Opera House. Things can't be going too badly, and she looks happy and full of life. There's even a short video of her playing and singing along to Bob Marley songs!