Will a woman who read palms jokingly and came to know unseen matters be forgiven, and how can atonement be made for this sin?

Claiming knowledge of the unseen through palmistry is a grave error, for none knows the unseen save Allah. You have sinned by consulting someone who claims knowledge of the unseen, for "whoever goes to a soothsayer and asks him about anything, his prayer will not be accepted for forty nights." As long as you have repented and regretted your action, Allah will accept your repentance. Strive in supplication, increase in good deeds and supererogatory acts of worship, and have a good opinion of Allah, for "the one who repents from sin is like one who has no sin."