Final answer:
The most likely diagnosis for a person extremely concerned about being grossly unattractive, especially after an accident, and fixated on their appearance is Body Dysmorphic Disorder (BDD).
Step-by-step explanation:
An individual who perceives that her body is grossly unattractive, especially following an accident, might be diagnosed with Body Dysmorphic Disorder (BDD). BDD is a mental health condition where a person spends a lot of time worrying about flaws in their appearance. These flaws are often unnoticeable to others. Given the information that the individual has developed a negative body image as the result of an accident and is extremely distraught about their appearance, BDD seems to be the most likely diagnosis.
While Post-Traumatic Stress Disorder (PTSD) could be considered due to the accident, the central concern related to her body image points more directly to BDD. Moreover, Major Depressive Disorder and Generalized Anxiety Disorder may have overlapping symptoms but do not specifically focus on body image concerns as BDD does. It is also notable that many individuals with BDD may also suffer from eating disorders such as anorexia nervosa, emphasizing the focus on body image.