While Missy Cooper went on to become a key figure in the overall "Big Bang Theory" franchise, Henggeler's original version of the character actually doesn't make that many appearances in the flagship show. In fact, Henggeler only guest-starred as Missy for two episodes across the entire series. What's even more surprising is that these appearances occurred roughly a decade apart from one another, in 2008 and 2018.

Henggeler's Missy first appeared in Season 1, Episode 15, titled "The Pork Chop Indeterminacy," and she returned in Season 11, Episode 24, titled "The Bow Tie Asymmetry." In her Season 1 debut, Missy comes to visit Sheldon, resulting in several members of the main gang developing crushes on her. Missy's second appearance in Season 11 sees her both pregnant and attending Sheldon's wedding — quite the narrative leap from her original appearance.

As she revealed in interviews at the time, Henggeler was nervous to return to "The Big Bang Theory" after a decade away. Nonetheless, she found the process to be far more comfortable than she imagined. "The best part of returning to 'The Big Bang Theory' was how warm and welcoming everyone was," the actor told BriefTake. "It's been 10 years since I last worked with that group (of insanely talented people) so I was a little nervous to go back. But that set is so lovely."