OMG - poor thing, you too...

Before you go down the supp path, try Movicol from the chemist... it is an oral powder that you mix with water and it helps soften as it draws the water that it is mixed with into the bowel and the poo.
There are two types of medications that are used, softeners (glycerine) and ones that help the peristaltic movements of the bowel (coloxyl)... increasing the fibre in the diet is going to help by providing bulk that will help stimulate the bowel to move the poo along, the big problem is that it is going to be bloody hard close to the end of the bowel and this is what is going to cause the pain when passing as it is all jammed together and will not squish out itms.

She needs loads of water, i would be diluting the juice with water as if it is too sugary, water may be pulled away from the bowel to dilute the sugar - and then you will have the opposite effect.

Hope this helps and she is pooing soon