Does a wife's concealment of her irregular menstrual cycle and the resulting inability to conceive affect the validity of the marriage, and does it nullify this marriage?

First: Delayed or absent menstruation leading to infertility is a purely medical matter.

Second: If the absence of menstruation leads to infertility, and your friend is aware of this, then she erred by not informing the suitor. This is because infertility is among the defects that must be disclosed. However, if it is a temporary condition, disclosure is not necessary. But if it is an influential illness, the guardian must inform the suitor about it. Concealment does not invalidate the marriage, but the husband has the right to annul it upon discovery.