My 45 year old sister is obese. She is experiencing sudden vision problems. Will she need to have a surgery?

Depends on cause. If obese, can have vascular issues and resultant vision changes, or idiopathic intracranial hypertension (commonly with transient visual obscurations), or vision changes associated with diabetes, etc.
Obesity w/vision los. Another factor to consider is pituitary adenomas as a cause of both obesity and vision loss.