People find the British aristocracy and its ranks and how one is supposed to address the various members of it confusing.
There are numerous websites out there that explain it. One of the most useful I have found in terms of pointing out some of the common errors made in historical fiction is this blog post by KJ Charles (whose own romances get it right and get the social constraints right). British Titles of Nobility is exceedingly thorough, but cops to being based on a 1932 reference source, by which time there was an entire thriving industry in writing etiquette books for the oiks on how their betters should be styled. Not sure how far one can read back conventions and practices! though also bearing in mind that these things had become fairly fossilised by then. A simpler outline is provided by English Heritage.
Clorinda was, it’s clear, a quick study, and would have seen the value of being attuned to the nuances of the system, but it is always possible that she made the occasional errour in style or designation when writing up her memoirs.
L.A. Hall, FRHistS