Plastic surgery is a surgical specialty involving the restoration, reconstruction, or alteration of the human body. It can be divided into two categories. The first is reconstructive surgery which includes craniofacial surgery, hand surgery, microsurgery, and the treatment of burns.
The operation itself is permissible but it must not involve any sinful act like a non Mahram man touching her or seeing her with out Hijab.
It is allowed to get plastic/cosmetic surgery.
Plastic surgery should not involve areas which are forbidden to be seen or touched by others like the private parts.
Other parts of the body should not be seen or touched by non Mahram (other gender).