Head on over to Rite-Aid and get some fiber gummies. They are for constipation. Give her only a half of one a day at first, or even a quarter of one, because if she has blockage you don't want to cause a well of liquid poop in her colon behind the blockage. In short, start slowly. But give her something to loosen up the stool.
It is also possible to do this with other things besides fiber gummies, but they are very reliable. You could try, for example, stewed plums. But it is hard to know how to manage the dose -- it would hurt her if you did too many.