The Unhuman Condition by Richard Levesque

After her research mission goes awry, Lespeth is desperate to go home and put the nightmare behind her.

Unfortunately for her, home is light years away.

Trapped in 1921 Hollywood, all she can do is find a way to blend in with the aliens who surround her until she can get back to her native planet. And that's going to mean dealing with the hoodlums, drug dealers and dope fiends who dwell on the city's dark edges.

She doesn't know that her journey is about far more than a safe homecoming. By the time Lespeth discovers that the fates of both her species and all of humanity are tied to the choices she makes—and the ones that more powerful entities have made for her—the path back to her planet may be closed to her forever.