Karen,
The unofficial record for lactational amenorrhea (no periods) is over 3 years.
 This mom was breastfeeding twins who were highly allergic to almost
everything (given formula as preemies..)so she was providing a good deal of
their nutrition.  I have heard moms go much more than one year nursing one
child.  There is a wide range of normal here.  As long as there are no
untoward symptoms, mom should relax and enjoy.
Catherine Watson Genna, IBCLC  NYC