One of the great mysteries on "The Big Bang Theory" is that after 9 seasons we still don't know Penny's maiden name. Since her marriage to Leonard she's now Penny Hofstadter, but she was previously and briefly married to Zach Johnson and arranged for that mistake to be annulled in the episode, "The Thanksgiving Decoupling." Penny is a streetwise farm girl who grew up in rural Nebraska but moved to California to pursue what can be best described as a dismal career in acting.
An aspiring actress
Although Penny has worked hard to become an actress she has never gotten her big break.
Her notable jobs in the field include castings in productions of "Rent" and "Anne Frank," as well as a role in "Serial Apeist" that contained a nude shower scene that featured Penny topless. Penny is devastated when she finally lands a small role on "NCIS" in "The Hesitation Ramification" and the scene is cut from the episode. This experience convinces Penny to abandon her career at the Cheesecake Factory and focus exclusively on acting.
Change of careers and social status
When acting doesn't pan out the way Penny expected, and her bills pile up, she accepts a job interview with Dr. Bernadette Rostenkowski-Wolowitz's pharmaceutical company for a position as a rep. Penny takes the job and excels at her position to the point where she is actually making a significantly higher wage than Leonard, which feeds into his insecurities.
Penny doesn't like the job as apharmaceutical rep but has extreme credit card debt so she's been toughing it out as an adult. Season 10 may see Penny change careers, but she's made it clear that she doesn't have an interest returning to her old waitress job or trying her hand as an actress again.
Marriage to Leonard
Simply stating that Penny and Leonard's relationship has been complicated over the last 9 seasons is an understatement.
Despite their past differences, and all the other relationships they've had between breakups, the two finally got married in Las Vegas at the start of season 9 and it appears that season 10 will be a redo of the wedding with Leonard's parents and Sheldon's mother in attendance. Notably missing are Penny's parents, although we've only met her father, Wyatt. In the last scene of season 9 Penny is shown laughing hysterically because Sheldon's mother has apparently hooked up with Leonard's father.