Dear Robin, this happens much more frequently than realized or acknowledged
by western/traditional medicine.  Moms do it for adopted babies.  In 3rd
world countries it is done for orphaned babies.  There is a whole body of
info on relactation. My file, which is by no means complete, is over 1/2 "
thick!  Most of these list articles from other sources. The oldest mom/baby
pair that I had experience with was beginning at 5 mo.  The baby had nursed
for the first few weeks.  Mom relacted fully over a period of 2 months.
This was in the days before the SNS and other neat tricks, donated milk and
milk bank milk was also used.  Baby was completely BF from mo. 7 to 10 and
continued nursing past 1st birthday.  Back in the early days of LLLI there
was a lot of notoriety about "mother's milk saves baby".  I believe that
mom relactated.  Sincerely, Pat in SNJ

Hormann, E.  Relactation: A guide to breastfeeding the adopted baby.
(1971). Probably out of print.

Sutherland, A. & Auerbach, K. G.  Relactation and induced lactation.
(1985).  Unit 1 of the Lactation Consultant Series, available from LLLI

Nursing an adopted baby.  Pumping Pointers No.6,  Ameda/Egnell, Inc.

Boyle, D.  Adoptive Nursing. (1993).  Leaven, Jan/Feb. 1993, p. 3-5, 10.