There is a wide natural variation in clitoris size, just as there is with penises, and large clitorises are not that unusual. Most likely*, the size of this woman's clitoris is due to that natural variation.
* There are medical conditions such as adrenal tumors that can cause abnormal enlargement of the clitoris, also hormonal supplements can cause enlargement.
My wife's friend had a benign adrenal tumor that caused to lactate and over the course of 6 months her clit grew 3x it's original size. She loved it, although was sometimes awkward in a bathing suit, if she became aroused.
