I think cutting down/stopping bfing caused constipation (perhaps a fissure as well) and triggered it too.
I read a good book on the subject written by a paediatrician who specialised in the area and luckily had a great GP who knew exactly how to treat it.
Before we had this GP, there were lots of mistakes made with stimulant laxatives (e.g. senna) which caused cramping and just made the whole situation a lot worse. By the time we were on the right road, his colon was so badly stretched that long term laxatives would have been necessary even if he stopped with-holding immediately 
We basically were on firstly an 'evacuation' dose of movicol to clear everything out and start from scratch. Then it was trying to find a daily dose which kept the stools soft enough that he couldn't hold them in, and slowly but surely he was reassured that there was no pain and his colon could return to normal. Getting the balance right took a little while. Eventually, we could gradually reduce the dosage as he had simply forgotten to hold it in (and the internal damage was repaired.
You will know if things are really bad as there will be encopresis - overflow diarrhoea - showing up as smeared pants. This happens as the colon is impacted.
Sorry if I'm explaining too much - you prob know all about it - I just get quite passionate about it as it was such a dreadful dreadful; thing to get under control and the quicker you get on the right road, the faster it will be solved.
It does sound as though you've caught it early though - so hopefully it will be a short-term thing for you all 
Whatever you do, don't let them give you stimulant laxatives - ideally she needs movicol but they will prob start with lactulose - best of luck with it 