I checked the Highland Co. Marriages (1805-1880) and didn't see any marriages after 1850 for a Sarah (or Sally) Sweney/Sweeney. There are several marriages for various Sarah Reeds, including the 13 June 1847 marriage to your Charles C. Sweney. I don't imagine she returned to using her maiden name tho.

I could find nothing on the Sweeney family in the Elsie Johnson Ayres books.