Moffat wasn't sure if Gina Bellman was right for the role of Jekyll's wife after working with her for four years on Coupling. Since that was a sitcom, he didn't think she could handle such a weighty, dramatic storyline. It made her more determined to win the role.
Gina Bellman doesn't enjoy working with props, because she always managed to damage them in TV shows like Coupling. But by the time of Jekyll, she managed to conquer that problem.