Diane:  I think you are right.  There is no need for the mom to wait for
the mammogram.  There would be no need to wait even if that breast was
still producing milk.  Although lactation can make the reading a little
more difficult to interpret, that should not be a reason not to do the
mammogram.  If a mother who is actively lactating needs a mammogram, she
should nurse or express just prior to the study.  Hope this helps.
Alicia.