The reason she says this is that it's mandated in the Koran, Sura 4.34:
As for women of whom you fear rebellion, convince them, and leave them apart in beds, and beat them. Then, if they obey you, do not seek a way against them. Surely, Allah is the Highest, the Greatest.
ADDED: A commenter Afeez A says: “The believers who show the most perfect Faith are those who have the best behaviour, and the best of you are those who are the best to their wives".Riyad as-Salihin 278”. And: “i hope you will read the link and will avoid posting "un-related / out of context" comments on any religion.”
To which I respond: whenever something in Islamic texts is unflattering to Islam we get the apologia that it’s “out of context”. Note that my quote is from the Quran, Afeez’s from a Hadith, less authoritative. And also, … sigh…