Has mom tried changing types of breast pumps i.e. if not using a Classic, try
it?  Have you looked at her pumping schedules?  What about B complex or
brewer's yeast?  Many times I've had moms complaining about low supply and on
further investigation, find they have been told by NICU (someone) they were
making too much milk and actually cut back to 5 or fewer pumps per day for
short periods.
On the progestin pill -- just had experience with mom who went on progestin
pill and found her supply to gradually diminish.  I have other threads to
this effect here on Lactnet.  What is the concensus at this point or is there
one?  I believe that there are many intertwining threads that affect supply
and all threads must be unwound.  No one factor alone can be addressed but a
"shotgun " approach that addresses latch, breast stimulation, diet and other
interfering factors.