Ibn Kathir states in his Tafsir (1/483): “But when the spouses fall into serious discord, the wife fails to fulfil the husband’s rights, she comes to detest him, and finds herself unable to live with him, she may ransom herself by returning what he had given her. There is no sin on her for paying it back, nor on him for accepting it.” End of quote. This is what is known as khulʿ, the compensatory divorce.

[If she asks for separation without any valid excuse, what warning applies to her?]
Q: If a woman requests separation from her husband without a legitimate reason, what warning has been reported regarding her?
A: Thawban reported that the Prophet ﷺ said, “Any woman who asks her husband for a divorce without suffering any harm will be forbidden the fragrance of Paradise.” (1)
Divorce is the most detested of lawful matters to Allah and should only be resorted to when necessity demands. Without such necessity it is disliked, because of the well-known harms that follow. The need that drives a woman to seek divorce is her husband’s refusal to fulfil her rights in a way that causes her genuine harm were she to remain with him. Allah the Exalted says, “Either keep [her] in kindness or release [her] graciously.” (al-Baqarah 2:229) (2)
He also says, “For those who swear not to approach their wives, there is a waiting period of four months; if they return [to their wives], Allah is All-Forgiving, Most Merciful. But if they resolve on divorce, Allah is All-Hearing, All-Knowing.” (al-Baqarah 2:226-227) (3)