Is it permissible for a woman to masturbate after intercourse or at any time if her husband does not satisfy her sexual desire, and is it permissible for her to do so with his permission?

The fundamental ruling on masturbation is that it is forbidden, and it is only permissible when there is a fear of falling into adultery.

If a married woman's sexual needs are not met, her husband should strive to caress her with his hand before intercourse. If she still has a need after intercourse, he should resume caressing her with his hand until her needs are satisfied. There is no harm in him consulting a doctor if he suffers from weakness.