Fiona,
I have found difficulties pumping around the time of menses to be common.  If
the mom is persistant, she might be able to pump more milk in a few days.  I
would also recommend that the mom examine the pump kit carefully, sometimes a
ripped valve will destroy the effectiveness of the pump.  Has she tried manual
expression?  Sometimes small pumps work well in the early days when breasts
are tighter, but when they soften ("settle down to do the job" as you aptly
put it)  the small pump is no longer effective.  This pump (N------ III) is
not my personal favorite, at any rate).
Catherine Watson Genna, IBCLC  NYC  [log in to unmask]