Question: Lady Margarita Elizabeth Rose Alleyne Armstrong-Jones is the only daughter of an English furniture maker who is 18th in line of succession to what?  
Sentence (from "David Armstrong-Jones, 2nd Earl of Snowdon"): David Albert Charles Armstrong-Jones, 2nd Earl of Snowdon (born 3 November 1961), styled as Viscount Linley until 2017 and known professionally as David Linley, is an English furniture maker and the former chairman of the auction house Christie's UK.
Relevant evidence: Yes