Jill Maughan is an author who wrote just the one pony book, as far as I am aware. She was born in 1958 in Newcastle-upon-Tyne, and has had various jobs including journalism and copywriting. Currently, she is working part-time at a school for boys with behavioural and emotional problems.
Deceivers is an interesting story: it’s about a riding school owner who is pretty unhinged, and is spectacularly lucky not be arrested. However, fortunately for the plot, she isn’t. Janey Squires, the riding school owner, is possibly one of the most unpleasant characters in children’s pony books. She is devious, manipulative, volatile and paranoid. And yes, she is just as bad as I’ve made her sound.
The book itself, which saw its first and only publication as an Armada original, is reasonably easy to find, and not usually expensive.
Literature North East (website no longer extant)