Are creams that contain skin lighteners considered prohibited, and is a Muslim woman sinful if she takes care of her skin with the aforementioned products or with preventative anti-wrinkle products and the like?

The basic ruling regarding the use of skin-whitening creams or anti-wrinkle creams is permissibility, unless their harm to the skin is proven. If their harm is proven, then they are prohibited, based on the Prophet's (peace be upon him) saying: "There is no harm [that is inflicted] and no reciprocal harm."