Stardust for Jennifer by Jane S. McIlvaine (1956)
Disappointed over Jim's sudden decision to work on a research project in New York, jennifer is caught up in the glitter of notoriety and the easy association with the famous stars, Sarina Swift and Jon Wiley--who are to play the roles of Jennifer and Jim. Then Jennifer, on her horse Chance, doubles for Sarina in a jumping sequence for the movie, gets her picture in Life and appears with Jon on a popular television program. She begins to feel as if she is on a merry-go-round, whirling faster and faster until the familiar details of life are nothing but a blur.
The dazzling effect of the unaccustomed publicity on the town, Jennifer and Jim brings unexpected complications yet Jennifer does not regret her brush with Hollywood. For it has given her greater perspective, a new humility, and she sees that she has grown up considerably during this exciting, if tempestuous, summer. (from the inside flap)