Nofia-In my experience, sudden onset of sore and especially cracked nipples
once breastfeeding has become well established is frequently caused by yeast,
whether visible or not.  The shells will probably not give her any relief if
that is the case.  I would treat homeopathically (see archives for discussion
of the acidophilous cure), and if that doesn't work, try a form of nystatin.
     Good luck with this.  Ellen in CT