Praise be to Allaah.
If a woman excites herself to the point of climax, it is obligatory (waajib) for her to do ghusl, and she is considered to be junub (in a state of sexual impurity) because of that. The Prophet (peace and blessings of Allaah be upon him) said: “Water is for water” (Saheeh Muslim, 151), i.e., ghusl becomes waajib when fluid is emitted as a result of sexual stimulation.
But this action – when a person excites herself or himself to the point of climax – is masturbation, which is forbidden for men and women alike. There is no differentiation between them in this regard. For more information and explanation of the evidence (daleel), please see Question #329.
And Allaah knows best.