Gall bladder pain is related to being post partum in many women. Has the mom
had an ultrasound to determine if she has a gall stone?  If the baby is
nursing as frequently as a newborn should and/or the mom is snacking
(especially if snacks are high fat) while nursing as is frequently and
justifiably recommended she may be precipitating gall bladder pain that way.
First thing is confirm if she has a stone.  Meanwhile you might recommend a
low fat, high fiber diet if there is no compelling reason not to do so.  If
she has gall stones this may make her more comfortable.

I would wonder if the hunger pangs we feel which may increase during nursing
are also part of a bigger precipitation of peristalissis in our gut even if
we don't eat and if this also causes the gall bladder to contract and causes
pain if it contains stone(s).  Any one knowledable about this hypothosis?