What must a believing girl do to expiate her sin after being subjected to harassment by a soothsayer to whom she went under the influence of her mother and her friend?

Your mother and your friend erred when they took you to the soothsayer, for it is forbidden and a grave evil, as the Prophet, peace and blessings be upon him, said: "Whoever goes to a soothsayer or a diviner and believes what he says, has disbelieved in what was revealed to Muhammad." Your going to him alone compounded the error, leading to ill intentions and wicked actions from the man.

Now that Allah has saved you from this matter and you have recognized your mistake, hasten to repent and be sincere in your intention to Allah, for Allah loves those who repent and forgives those who repent, believe, and do righteous deeds. If you abandon the sin, regret it, resolve not to return to it, and commit to obedience out of fear and hope, you will have achieved the required repentance. So rejoice and be steadfast, and do not worry, for the one who repents from sin is like one who has no sin. Do not tell anyone what happened to you.