Jacobs was cast as Donna immediately after leaving drama school, and considers herself "completely blessed" for having won the role. She was cast alongside fellow series six newcomer Kelly Adams, as midwife Mickie Hendrie. A BBC documentary entitled "Making It at Holby" chronicled their casting process, which entailed seven weeks of auditions, including group workshops to allow the series producers to gauge candidates' personalities. Adams originally auditioned as Donna, however the casting directors felt that she would be better suited to Mickie, the quieter character, and "mild mannered" counterpart to Donna's "sassy staff nurse". She and Jacobs were paired together during a three-hour workshop, and the producers detected an "instant spark" between them, leading to their dual casting. Following her successful audition, Jacobs was mentored by actress Jan Pearson, who played ward sister Kath Fox.