What a very special situation this is, one sister having a baby for the
other! Have you thought of manual expression instead of pumping (more skin
to skin stimulation, more like "the real thing" and easier to catch those
precious first few drops in a small cup than on the larger surface area of a
pump).  I have worked with a couple of adoptive moms who had some success
with gentle breast massage, then manual expression, minimum 8 times/24 hours
and medication with sulpiride (similar to metoclopramide) 50 mg three
times/day to raise prolactin levels.  Other things which I feel sure will
help are lots of physical cossetting and spoiling, e g massage all over,
long luxurious baths, loving touch by husband - anything which makes
prospective mother feel warm and special and female.

Best wishes, please keep us informed.

Pamela Morrison IBCLC, Zimbabwe