In Caroline Canters Home (1977), Caroline goes to stay with her cousins, having decided she wants a career in showing. The Harrisons immediately decide that Caroline is the ideal person to show their hack, Clytie. Caroline is not so sure. But at least Clytie has a lovely character, unlike Becky's pony, Benjamin, who is beautiful but vile. Benjamin is kidnapped by unwary villains, who certainly get everything that is coming to them.
Caroline Canters Home originally appeared in serial form in PONY, and it is pretty much what Stuart Hollings and I read in the early 1970s. Confusingly, it was published after the two showing books Hodder commissioned from Caroline, Caroline Canters Home and I'd Rather Not Gallop, but it is, in terms of the chronology of the story, the first.
The Showing series
Caroline Canters Home