Not sure if I should post it here, because it's not as much as the case of "one step further" as "more". I couldn't find a thread about one-time wonders.
Betty Jean Bradley had the figure and looks of the most popular stars of her time.
She was the star (cover & all - and it wasn't some cheap gonzo porn) of
Blow Job Betty in 1991, where she did 3 scenes: lesbian, blowjob (twice, including sucking famous Rocco) and then... she disappeared.