"The Warslayer" by Rosemary Edghill
Glory is an ex-Olympic gymnast and plays Vixen the Slayer a 16th Century equivalent of Buffy, and she is currently on a promotional tour of the United States when a trio of mages materialise in her dressing room and ask her to save their world. It seems all the other heroes they've asked have turned them down and she is their last hope. Glory stumbles through an explanation that she isn't really Vixen, that Vixen is just a story, made up for entertainment. The mages sadly prepare to depart but their magic goes wrong and brings Glory with them.
In some ways this is a typical 'growing up' story - Glory finds out things about herself, and meets the challenges set before her. There are some good plot twists, and the feat she must do is not, in the end, the one you expect - indeed it is ambiguous if she has done the 'right' thing. It also manages to avoid the cliched love story (though if you pay attention there are hints there). A fun, and somewhat whimsical, story - and I suspect if I had watched more Buffy there would be more in-jokes to notice.