**Core Concept**
The patient's inability to extend, adduct, and internally rotate her arm suggests a weakness in the muscles responsible for these movements, specifically those involved in the scapular rotation and shoulder joint extension.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with a paralysis of the latissimus dorsi muscle. This muscle plays a crucial role in adduction, extension, and internal rotation of the shoulder joint. The latissimus dorsi muscle originates from the spinous processes of the thoracic and lumbar vertebrae and inserts into the bicipital groove of the humerus. It is innervated by the thoracodorsal nerve, a branch of the posterior cord of the brachial plexus.

**Why Each Wrong Option is Incorrect**
* **Option A:** Teres major muscle is involved in adduction and internal rotation of the shoulder joint, but it is not primarily responsible for extension. It is also innervated by the lower subscapular nerve, a branch of the posterior cord of the brachial plexus.
* **Option B:** Pectoralis major muscle is involved in movements such as flexion, adduction, and medial rotation of the shoulder joint, but it is not primarily responsible for extension. It is innervated by the lateral pectoral nerve and the medial pectoral nerve.
* **Option D:** Rhomboids muscle is involved in scapular rotation and fixation to the thoracic wall, but it is not primarily responsible for shoulder joint extension.

**Clinical Pearl / High-Yield Fact**
The latissimus dorsi muscle is a key muscle in the posterior wall of the axilla and is often involved in axillary dissections for breast cancer surgery.

**Correct Answer:** C. Latissimus dorsi