Is it permissible for a woman to seek divorce because her husband wishes to marry another woman, due to her inability to bear him a son, despite their having four daughters, and what is the legal ruling in Islamic law regarding her request for divorce?

For a woman to request a divorce for a legitimate reason is not blameworthy. However, it is unlawful for her to request it without a valid cause. A man marrying another woman while already married is not a harm that permits the wife to seek divorce. But if she is harmed by it, then she may request it. The husband is not obliged to grant her a divorce unless she stipulated it in the marriage contract; in that case, she has the right to annul the marriage.