This might be it.
Gravity by Magz
Summary: As one of the leading physical therapists in the country, Buffy Summers gets to work with some of the most famous athletes in professional sports. She's never contemplated turning anyone down – until her little sister pleads with her to work on William ["Spike"] Broad [hehe... notice the Billy Idol reference] - the world's most famous rock climber, and a man that she's disliked since their first meeting five years ago. Unfortunately for Buffy, her sister is very good at persuasive tactics, and the blonde soon finds herself shipped off to California with all her belongings, prepared to move into William's lush mansion to give him all the therapy he needs to get back on his feet. Based on the novel Adam's Fall by Sandra Brown.
http://www.sinister-attraction.net/stories/m/gravity.htm
