Bonnie,
Paraphrased a little here's what caught my eye:
<<Baby weighed just over 6 pounds at birth, lost a few ounces in the
hospital and regained birth weight by 2 weeks of age.  At 6 week
check-up baby weighed 8 lb.
Mom stated her nipples were sore, and baby never seemed satisfied.
When I arrived, I immediately noted baby was thin though not dehydrated.
She cried most of the 2 1/2 hours I was in the home, except for when she was
at the breast.
put to breast,  I noted a shallow latch.
sucking was almost entirely "non-nutritive" >>
Plus you said mom expressed a cup of milk but couldn't pump anything (did I
read this wrong?)

This sounds very much like what my partner and I call *Second Stage
Overactive.* Woolridge described some infants who became failure to thrive
after a period of an apparently abundant milk supply and great weight gain.
What we've seen is babies who develop a shallow, sometimes clamping latch,
which we assume is a defense mechanism to keep from choking on mom's milk.
Baby's intake is barely anything, lack of breast emptying causes the supply to
decrease but the baby maintains the poor latch. Hence it becomes a downward
spiral.
What to do: Fix the latch, increase the supply and use an SNS in the meantime.
If the heavy letdown returns (and it often does) baby will revert back to the
poor latch. Mom should watch for baby having problems with the milk flow and
take necessary steps (like not switching breasts and/or pumping off the first
letdown etc...)
BTW in second stage overactive we often see outright breast refusal as well.
Marie Davis, RN, IBCLC