In our Fiqh, a wet-dream is called Ihtilam, (from the word hilm, which means dream). A wet-dream is one of the signs of religious maturity for a male, and its general definition is "the ejaculation of semen while sleeping."
Naturally a wet-dream occurs for both males and females, but there is a view that a woman does not have to do ghusl janabah when she has a wet-dream, and discharge.
Most of our esteemed Jurists do believe that a woman must do ghusl janabah if she has a wet dream, on the condition that she has a discharge of sexual fluid from an ejaculation/orgasm.
This means that in the wet-dream, if there is no discharge ghusl is not wajib.
Another important point is that according to most Jurists, the sexual fluid that emmits from an orgasm is considered to be Najis (impure).
And Allah knows best.