Rachel McAdams part in Sherlock Holmes?

Rachel McAdams did not appear in any of the "Sherlock Holmes" films starring Robert Downey Jr.

The female lead roles in those films were played by:

* "Sherlock Holmes" (2009): Irene Adler, played by Rachel McAdams.

* "Sherlock Holmes: A Game of Shadows" (2011): Irene Adler, again played by Rachel McAdams.

Perhaps you are thinking of a different film?