Pam,
I am not a doctor and I am only sharing my personal experience with you.I
have had two UTI in the last three years( while nursing) and have never used
pyridium. With antibiotics and LOTS of fluids the pain of UTI should be gone
within 12-24hrs.(or sooner). Also found chewable cranberry tablets with
vitamin C to be helpful too.Plus 24hrs. bedrest. The Homeopathic remedy for
UTI is Cantharis (clear up pain very rapidly).  If mom is familiar with
homeopathy she will probably have a reference book telling her about this
remedy. No need to interupt nursing. I'll bet if she asked OB if pyridium was
really necessary he would say no, just take the antibiotic. She should tell
him she doesn't want to interupt BF and see what he says.
Hope this helps.
Robin