It looks to me as though you are interpreting the introduction correctly and I think she should be keyed as Sarah W Arnold with spouse surname = Beane. (FamilySearch has a marriage at Barrington 14 Nov 1861 between Sarah W Arnold and Benson Bean to confirm this is what they mean).

That "b" abbreviation looks likely to cause confusion! Hopefully if they go through as baptisms instead of "other" it isn't likely to be a major problem for researchers, though.