What should a woman do whose husband has been absent for nearly four years, then married another and abandoned her, so she committed the sin of adultery after filing a khul’ lawsuit?

The husband's abandonment of his wife is not a justification for her to commit indecency, for fornication is one of the gravest sins. However, no matter how great the sin, Allah accepts sincere repentance which involves abandoning the sin, regretting it, and resolving not to return to it, while concealing one's sin. It is permissible for a woman to seek divorce from a husband who neglects her rights.