Mrs Keppel indicates a simple commoner, but Alice herself was the daughter of the 4th Baron Edmonstone and was born at their estate, Duntreath Castle at pittoresque Loch Lomond (
picture).
Her husband, the Hon. George Keppel, indicates a commoner, but he was the son of the 7th Earl of Albemarle. The (Van) Keppels are 15th C nobles from the Netherlands. The original Van Keppel castle is still there, in the place named Keppel and is still in private ownership of Van Keppel-ancestors:
front view.
So technically a commoner or not, Camilla's parents and grandparents were not "from the street" so to say.