One of the most selfish reasons I've breastfed for as long as my
children wanted to was to keep my severe endometriosis at bay.  The
whole point of drug treatment for the problem, in my simple
understanding, is to prevent ovulation, thus, OCs are sometimes used
w/out the usual "days off" to force a period.  I had several infertility
docs say to *avoid* estrogen w/ my endometriosis; granted, that simply
may have been their preference?  A side effect of breastfeeding was that
I did not experience the usual endometriosis symptoms when my menses did
return; my dh found it quite a blessing, as well, since he could
actually stand to be in the same house w/ me for the entire month and
that was *not* the case pre-pregnancy/pre-breastfeeding even w/ a lap
and some hormonal treatments.

If the client's not menstruating, she's probably asymptomatic and I'd
just use the LAM guidelines since they help delay the return of
fertility and, possibly, her symptoms.  Also, if she wants more children
down the road, she may be urged to wean before she or her child is
ready...interesting anecdotes over the last few weeks on the listserv to
the contrary...Good luck!

Rebecca DeYoung Daniels, MBA, RD, LD, LLLL in Overland Park, KS...but
writing this as "just a mom" who was told the severity of my
endometriosis would prevent me from ever having children...now there are
2 and 1 due in a few months :-)