You might want to post on the bowel disorders board also.
My non-professional guess (though I have had the condition myself) is that probiotics would help prevent or at least defer development of diverticuli, but once they have developed and certainly once they have become infected they would not help much to alleviate symptoms.
Is your mum a candidate for a bowel resection? That may certainly help symptoms and probiotics then might help prevent problems from recurring.
