Is a woman who sought divorce from her husband because he refused to give her the full mahr (bridal gift) sinful, and what is the expiation for that?

Marrying more than one woman is a legitimate right for a man, provided he deals justly between his wives in terms of spending, lodging, and good treatment.

Neither the wife nor her family have the right to demand a divorce or burden the husband with financial demands when he marries another, without clear harm; for divorce is the most detestable of permissible acts to Allah, and he is not of the Muslims who corrupt the relationship between a husband and wife.

A woman who seeks divorce without a legitimate reason will be deprived of the scent of Paradise.

If the aforementioned woman caused her husband's separation without a legitimate reason, she must repent and seek forgiveness. She may request to return to him; if she is within her waiting period ('iddah), it is without a new contract or dowry, but if her waiting period has ended, then it is with a new contract and dowry.