What is the ruling on wearing an abaya or a long skirt with a bottom slit that reveals part of the leg, and what is the ruling on that if she is wearing a sock that covers the slit?

There is no specific dress required for the legal hijab (Islamic veil). Any attire that fulfills the conditions of legal dress is considered a valid hijab in the Sharia. There is no objection to an open abaya if it does not reveal any part of the body or any adornment; otherwise, it is forbidden. The dress must cover all parts of the body, be loose so as not to define any part of the body, and be opaque so as not to reveal the color of the skin. Therefore, if the abaya is tight, outlining the body's parts, or if it exposes the legs, which are not covered except by socks that outline them, then it is not permissible to wear it in front of non-mahram men.