**Core Concept**
The management of fracture neck femur in an elderly patient involves a delicate balance between maintaining hip function, preventing complications, and ensuring a good quality of life. The treatment options vary depending on the patient's age, activity level, and the severity of the fracture.

**Why the Correct Answer is Right**
The best treatment for a fracture neck femur in a 65-year-old lady is often internal fixation with a sliding hip screw (SHS). This approach allows for early mobilization, reduces the risk of avascular necrosis, and promotes bone healing. The SHS device provides stable fixation while allowing for some degree of femoral head subsidence, which is essential for maintaining hip function in elderly patients.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect as it does not address the specific needs of an elderly patient with a fracture neck femur. The patient's age and activity level are crucial factors in determining the most suitable treatment.

**Option B:**
This option is incorrect as it may not provide adequate stability for the fracture, leading to complications such as nonunion or malunion. Internal fixation is generally preferred over nonoperative management in elderly patients.

**Option C:**
This option is incorrect as it may lead to prolonged immobilization, which can result in complications such as deep vein thrombosis, pressure sores, and loss of hip function.

**Clinical Pearl / High-Yield Fact**
In elderly patients with a fracture neck femur, it is essential to consider the patient's quality of life and functional status when selecting a treatment option. Internal fixation with a sliding hip screw is often the best choice, as it allows for early mobilization and promotes hip function.

**Correct Answer: C. Intramedullary nailing.**