Rosenberg, 48, started writing seriously in 1991 after a six-year stint as a Ventura, Calif., law enforcement officer. Her three legal thrillers - Mitigating Circumstances, Interest Of Justice, and First Offense, all based on actual cases - have caused her to be compared with the likes of Scott Turow and have all been best-sellers, leaving her room to take risks. Rosenberg's latest novel, California Angel (Dutton), ventures far from the formula that has brought her

success. "It's about a dying woman who finds she can perform miracles," says the author.
    Her muse this time was Janelle Garcia, 18, born with a deadly genetic disorder that usually claims its victims in infancy. Known as MMA, short for methylmalonic acidemia, the disease causes the body to convert protein into a toxin similar to antifreeze. Janelle, who lives in Santa Ana, Calif., with her severely arthritic mother and has been tube-fed most of her life, has survived longer than any other known MMA patient. "Janelle is so courageous," says Rosenberg, who became the teenager's friend and benefactor after Rosenberg's rabbi introduced them in 1992. "You can feel a divine presence around her." says Janelle, who is often