Janet Trench was born 24th May 1820. Family legend has it that she was one of four daughters to Richard Le Poer Trench, 2nd Earl of Clancarty. But I can find names for only two daughters in Burke's. Nor can I find her named in Burke's as one of six daughters to Richard's brother the Very Revd Power le Poer Trench, Archbishop of Tuam (not helped by fact that Burke's names only one daughter of the six). These numbers, four and six, are from the Dictionary of National Biography.
The St John family bible shows that Janet definitely married Captain James Henry (Humphrey?) St. John, Royal Artillery, on 18th December 1837. Maybe in Jamaica. They definitely had six children: Mary (1838-?), William (1839-?), Jane Anna (1841-1903), Catherine Sutton (1843-1858), Janet Keane (1844-1932), and Carolina Turner (1846-1886). Probably most of them born in Jamaica. Janet Keane married deputy Surgeon-General William Skeen. She was my father's "Big Granny" and father to two soldiers (General Sir Andrew Skeen and Major Oliver St.John Skeen, DSO) and to four doctors.
Burke's definitely shows James Henry St John (1798-1846), Captain RA, as a descended, through another Henry (?-1834), from Henry St John (?-1780). The latter was Captain in the RN and third son of John St John 11th Baron St John of Bletso (1702-1757). Captain Henry married Mary Schuyler (?-1786) of New York, whose father was a BIG noise in the American War of Independence. On the American side.
The questions I have are - Do your Trench family records accord with any of this? Is Janet from the Clancarty Trench's? And if not then where from?