**Core Concept**
The patient's presentation is consistent with Sheehan's syndrome, a rare but serious complication of postpartum hemorrhage and abruptio placentae. This condition is characterized by necrosis of the pituitary gland due to severe blood loss, leading to hypopituitarism.

**Why the Correct Answer is Right**
The necrosis of the pituitary gland results in the destruction of the anterior pituitary gland, which is responsible for the production of various hormones, including growth hormone, prolactin, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). The destruction of these hormone-producing cells leads to a deficiency in their production, resulting in symptoms such as muscle weakness, failure of lactation, and amenorrhea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it refers to a different condition, known as postpartum thyroiditis, which is characterized by inflammation of the thyroid gland and can lead to transient hypothyroidism or hyperthyroidism.

**Option B:** This option is incorrect because it refers to a condition known as postpartum depression, which is characterized by a mood disorder that can occur after childbirth, but is not related to the patient's symptoms.

**Option C:** This option is incorrect because it refers to a condition known as postpartum preeclampsia, which is characterized by high blood pressure and proteinuria after childbirth, but is not related to the patient's symptoms.

**Clinical Pearl / High-Yield Fact**
Sheehan's syndrome is a rare but serious complication of postpartum hemorrhage and abruptio placentae, and can be prevented by prompt and adequate treatment of postpartum hemorrhage.

**Correct Answer:** C. Necrosis of the pituitary gland.