I think it's ok to give her with foods.
I'm no expert, but I have IBS with constipation and I use raw goat milk kefir every evening. It helps tremendously but you have to let it ferment only 24hours max.
I also drink plenty of water.
But you seem to do fine with the oat bran and kefir.
Fresh figs are also know as laxative.
But this maybe won't solve the cause if there is one.
Hope this will work with slippery elm.
Marshmallow root is also good to soothe the stools as it forms bulks.
Seaweeds give moisture in the intestines and support the thyroid, as hypothyroidism can lead to constipation.