A somewhat similar case is mentioned by Gregory of a mother of 7 children who had never had her menstrual flow.

There are two instances of delayed menstruation quoted: the first, a woman of thirty, well formed, healthy, of good social position, and with all the signs of puberty except menstruation, which had never appeared; the second, a married woman of forty-two, who throughout a healthy connubial life had never menstruated.

An instance is known to the authors of a woman of forty who has never menstruated, though she is of exceptional vigor and development.

She has been married many years without pregnancy.
The medical literature relative to precocious impregnation is full of marvelous instances.

Individually, many of the cases would be beyond credibility, but when instance after instance is reported by reliable authorities we must accept the possibility of their occurrence, even if we doubt the statements of some of the authorities.