Mark,
Your latest chapter is a fine description of the rules governing the upper classes at the time. There were about 1000 families who were closely interrelated and between them controlled almost everything. So Caroline has been effectively banished from society. Nobody except her own family, and not even all of them would have supported her if she tried to stay in London. Many in her position were almost destitute or went to live abroad or in the colonies. Divorce was only available to very rich men (not to women) and involved a law case against the other man, a decree of judicial separation (called divorce but it did not permit re marriage) and a private act of Parliament.
However, Lord Castlereagh and Charles Stewart were half brothers and the sons of the marquis of Londonderry, not Lord Liverpool, who was only 5 or 6 years older than Granger.
Looking forward to the next chapter.