All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
There is no harm on wearing a wig for a woman who had hair loss from cancer conditioned to be worn inside her house and by the knowledge of her husband, so long as it is neither made from human or impure hair nor worn in front of non-Mahrams (Marriageable men) as it is considered kind of adornment.
Further, she is permitted to treat herself by having hair plugs for it is not considered a change in Allah’s Creation; rather, it is a kind of therapy by which she will have her genuine figure which is Created By Allah, The Exalted as been stated by the International Islamic Assembly No. (173) for 2007 AD regarding plastic surgery: ”Making urgent plastic surgery such as: skin grafts and hair plugs particularly for women in order to fix the damages resulted from accidents, burns and illnesses...etc is permissible.”
However, wiping over the wig while making ablution won’t suffice because it is not considered a part of the head similar to turban whereas jurists stated that wiping over the turban while making ablution won’t suffice and the ablution won’t be valid in the aforementioned cases. In this regard, Al-Imam An-Nawawi (May Allah have mercy on his soul) stated: ’’The completion of person’s ablution while wearing a turban is wiping both the turban and the forelock since it is an act of Sunnah, yet wiping only one of them while making ablution won’t suffice for a valid one at all.” [Rawdat At-Talebeen vol.1 pp.60]. And Allah knows best.