Is it permissible for a woman to seek divorce from her husband who mistreats her and reveals her past secrets to others, knowing that he demands the full return of the dowry, and her family cannot afford it, and that her maternal aunt disposed of a large portion of the dowry?

You have done well by regretting, and you must make it a sincere repentance. You erred by telling your husband what happened; it was incumbent upon you to conceal it. So, whoever is afflicted with such filth should conceal himself with Allah's concealment. We advise wisdom in solving the problem. It is not permissible for your husband to hit you without a legitimate religious reason, or to assume ill of you without clear proof, or to tell anyone what happened. It is also not permissible for him to abuse your mother. He is required to do one of two things: either retain you honorably or release you kindly. If he divorces you, he has no right to the dowry. If you seek divorce (khul') due to disliking his companionship, he has the right to demand compensation. If your maternal aunt took anything from the dowry without your permission, she must return it to you, as the dowry is the wife's right.