What is the ruling of the Sharia on the wife admitting the husband's brother in his absence?

The husband's brother is a stranger (non-mahram) to his brother's wife, and it is not permissible for him to be alone with her in seclusion. It is not permissible for a woman to allow a stranger to enter upon her when she is alone, due to the Prophet's (peace be upon him) saying: "Beware of entering upon women," and his saying concerning the hamw (the husband's brother and similar relatives): "The hamw is death." As also narrated in the hadith: "No man should be alone with a woman unless there is a mahram with her," and because the devil is the third of two. The sin increases if the husband dislikes that, due to the Prophet's (peace be upon him) saying: "And as for your rights over your women, they should not allow anyone you dislike to step on your فرش [beds/furniture, metaphorically] nor permit anyone you dislike into your homes."