Catherwood was initially told little about her character's background. She was made aware that Penny is "closed down" to men and relationships, in contrast to Oliver who has frequent affairs, but only had "an inkling" of why that was the case. During the show's twelfth series, Penny falls in love with heart transplant patient Scott James (Joshua Bowman), with Catherwood assessing that Scott "forces her to open her heart". Forced to decide between Scott and her career, Penny chooses love, which Catherwood described as "a huge thing to do". Although Scott ultimately breaks up with Penny on Oliver's advice, Catherwood felt that the development actually made the siblings' relationship stronger, explaining: "You forgive your family for an enormous amount. He's there as soon as she breaks down, he's there to catch her, full of apologies and support. It's just another thing that brothers and sisters go through and support each other through." Catherwood felt that the storyline would make Penny more driven with regards to her work, assessing that she had formerly been mistaken in being so confident and ambitious. She believed that Penny had been "shaken" by her rejection, which would lead to her becoming more vulnerable both personally and professionally. The actress hoped that Penny would improve at her job in the future, though commented that none of the remaining "Holby City" characters were a suitable match for her romantically. Penny arrives at Holby General as a Foundation House Officer 1, alongside her brother Oliver. Registrar Jac Naylor takes an instant dislike to her, and ignores her request to work on the hospital's Acute Assessment Unit, placing her instead on the general surgery ward, Keller. After making a good impression on cardiothoracic consultant Connie Beauchamp (Amanda Mealing), Penny is transferred to the cardiothoracic surgery ward, Darwin, where she is mentored by consultant surgeon Elliot Hope (Paul Bradley). Penny develops feelings for Scott James, a patient awaiting a heart transplant, and the two begin a relationship. During an unrelated case, Penny convinces a reluctant husband to donate his deceased wife's organs, unaware that Scott will be the recipient of her heart. When Elliot discovers their relationship and the link between cases, he holds Penny back a surgical rotation and forbids her to see Scott again. Scott announces his intention to move to Spain, and asks Penny to leave with him. Disillusioned with medicine, Penny agrees; however, Oliver convinces Scott that Penny will come to regret abandoning her career, and Scott rescinds his offer, leaving alone.