**Core Concept**
Primary amenorrhea with ambiguous genitalia in a female with 46XX chromosome typically presents a challenge in diagnosis. This condition arises due to the presence of excess androgen during fetal development, leading to virilization of external genitalia. The most common cause is related to an excess of androgen production.

**Why the Correct Answer is Right**
The correct answer is related to Congenital Adrenal Hyperplasia (CAH), specifically due to 21-hydroxylase deficiency. This enzyme deficiency leads to an accumulation of 17-hydroxyprogesterone (17-OHP), which is then converted to androgens, causing virilization. The excess androgen production is due to the shunting of cholesterol to the androgen pathway, bypassing the 21-hydroxylase step.

**Why Each Wrong Option is Incorrect**
* **Option A:** Androgen Insensitivity Syndrome (AIS) typically presents with a 46XY chromosome, not 46XX, as the individual has a mutation in the androgen receptor gene, making them unresponsive to androgens.
* **Option B:** Mayer-Rokitansky-Küster-Hauser (MRKH) syndrome is characterized by the absence or underdevelopment of the vagina and uterus, but it does not involve virilization of the external genitalia.
* **Option D:** Swyer syndrome is a condition where a 46XY individual has a mutation in the SRY gene, leading to gonadal dysgenesis and a female phenotype, but it is not associated with 46XX chromosome.

**Clinical Pearl / High-Yield Fact**
It is essential to note that CAH due to 21-hydroxylase deficiency can also present with salt wasting, hypotension, and shock in the neonatal period, making it crucial to consider this diagnosis in any female infant with ambiguous genitalia and electrolyte imbalances.

**Correct Answer: C.**