Diane,
Why should clarithromycin be any more dangerous to a nursling than any other
erythromycin derivative?  Notice the doc is not recommending pump and dump,
but weaning.  Maybe it is a good excuse?  One thing I would warn your mom to
look out for is thrush, in my experience clarithromycin use is likely to
result in candidiasis.
Catherine Watson Genna, IBCLC