examples of insoluble fiber are wheat bran, carrots, pumpkin, zucchini, sweet potatoes, spinach and celery. the speeding up of the transit time is good
for mega colon, however again you will need to be sure she empties her bowels frequently so the increase in stool size doesn't further stretch her bowel.
therefore moderation is the key.
your earlier post regarding lactulose. Its safe to give up to 2mls by dropper followed by 4mls of water, the water is very important.