TRIX: Raising your voice during high tea, whoever heard of such a thing? It’s like Fergie all over again.
Trix is referring to Sarah, Duchess of York (born Sarah Ferguson in 1959), a British royal known as “Fergie” by the British press. She married Prince Andrew in 1986; after having two daughters, they separated in 1992, and divorced in 1996.
Fergie’s demeanour as a royal was always very casual, and she could be loud and exuberant socially, which people either found a breath of fresh air, or like Trix, rather vulgar. We can see from her comment that Trix has been in high society in London, although the fact that she calls the duchess by her “press name” betrays that she doesn’t really know her at all.