I heard this once....that it would be difficult for a Lactose Intolerant
mother to nurse,  I believe that the issue was nutritional.  The belief
that somehow you need to "drink milk to make milk"

Crazy talk.  Vegans nurse.   Many Asian or Native North American
mothers are Lactose intolerant....they nurse,  some cultures
simply don't drink milk.  Good nutrition is an issue,  milk is not.
We are the only species to drink the milk of another.

Cows eat grass for crying out loud.

Stephanie Pearl, IBCLC and lactose intolerant
in Toronto, Canada.