OK we're now discussing two things but for the benefit of the OP a summary is as follows:

-Discretionary right of C permit for all since 2007 after 5 years, HOWEVER new rights brings new obligations, you must show you are integrated which may mean language assessment, uninterrupted work history, credit check, reference etc.

-Automatic right after 10 subject to normal background checks as above

-Regarding marriage, the C permit entitlement is after 5 years residence and 3 years marriage, time of residence from issue if B permit, time of marriage obvious.

-Regarding citizenship either 6 years married together outside CH, or 3 inside IF also resident in CH five years. (Similar to C).

The only benefit to the OP's friend's case is the type of permit is recorded on the citizenship application. It may be helpful to have a C at application as this demonstrates integration. Alternatively perhaps the requirements for facilitated naturalisation are easier as they haven't changed unlike those for a C permit which have since 2007.

That might help the OP's friend decide.

Bear in mind, although Americans etc. have special arrangements on C permit possibilities, they are still subject to integration requirements etc as are EU and non-EU nationals. Of course this may be controlled differently, for example an ex-colleague of mine from UK who has had the same job since arriving 9 years ago, was required to supply the higher credit report in addition to employment history etc, and she speaks German and hasn't left Zürich city.
Her UK husband already had a C permit, and her son received one on birth here, as did her daughter....go figure.