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Rauch joined the show last year as Bernadette, a love interest for Howard (Simon Helberg).
Entertainment Weekly says that the actress, who originally signed up for a couple of episodes, has now become a full cast member on the show.
Rauch's deal does not mean that she will be in every episode and it is not yet clear whether she will remain a regular after this season.
Rauch has previously appeared on Kath & Kim and played Summer in the third season of True Blood.
The Big Bang Theory continues on Thursdays at 8/7c on CBS.
