Breastfeeding causes uterine contraction in a very similar manner as does
orgasm duringt intercourse. Is this fertility MD telling her that she can't
have sex after IVF? For how long? Only if he/she is so concerned about
contractions that he forbids sex would it make sense that she has to wean.

Yes the hormones could dry up her milk but at four years how much is her
child getting? She is nursing mostly for the emotional bond with her mother
- the ounces of milk that she gets are a bonus.

My thoughts on the matter.