It would depend a lot on how fast her digestive system is, especailly her colon. With diarrhea or loose stool, it'll fall apart in the water and see all the bits and parts of what we don't usually digest (insoluble fibre) which is usually together in a solid stool.
It definitely could be IBS. If she's having increased frequency and urgency with rectal discomfort during bms, I'd say something more could be going on....but IBSers do have frequency and urgency as well.
Is she consuming artificial sweeteners? This is a most important point that many people seem to not even consider.
Is she expecting her period soon? The prostaglandins in the system will cause the colon to quicken a lot.
The best thing would be for her to see a gastroenterologist and push for a c-scope (based on your diagnosis and her symptoms) and be properly checked...biopsies included...plus stool samples to make sure she hasn't picked up anything wonky.
Was she recently on antibiotics?
She should, however, consider to use probiotics and a fibre supplement and see if her symptoms improve.
*Heather*Status: mini flare Dec 28... tapered to every 4th night
~diagnosed January 1989 UC (proctosigmoiditis)
~5ASA: Asacol (6 daily) + Salofalk enemas (increase for flares tapered to maintenance)
~Bentylol (dicyclomine) 20mg as needed
~Probiotic 3(Natural Factors Protec) bedtime + 1 (Primadophilus Reuteri) occasionally
~multi-digestive enzymes as needed ....zymactive 3 - 5x daily
~Ranitidine,Pariet (reflux) Effexor XR 75mg; Pulmicort/Airomir (asthma)
~URSO for PSC (or PBC) 500mg X 2 daily (LFTs back to NORMAL!!)
My doc's logic.. "TREAT (FROM)BOTH ENDS" worth it !!!