I've seen this one time, in 20+ years of assisting mothers to breastfeed.
Unfortunately, it was a long time ago, when we had much less information to
assist us in our work.  I was a hospital-based LC at the time, working with
HCPs who were very uninterested in and uneducated about breastfeeding, so I
just had to wing it.

Lactogenisis was *very* slow.  Fortunately, these parents were very motivated.
They had experienced years of infertility and were anxious to do everything
"right".  We supplemented, at breast, for weeks.  Eventually the mother was
nursing without the supplements, but her supply was always borderline and I
never relaxed with that one.  The only drug they gave her was benadryl, to
help with all of the itching, which lasted about 2 weeks.  She took as little
as possible, because of concerns about supply.  I would doubt that your client
will need as intense treatment as they are predicting, precisely because of
what Jack said about the progesterone drop.

Since then, I've wondered if the supply problems had more to do with hormonal
imbalance (a la infertility issues).  And of course, if I knew as much about
increasing supply, would we have had an easier go of it.  But I'll never know.

Nancy Williams