Sounds like an inflammation of the colon. This is what I would do:-
Put her onto professional pro-biotics Protexin Professional and keep her on it permanently for the time being.
1. Three days Panancur then repeat after three weeks (for giardia). Does not always show up in fecals.
2. Then if the bloody stool is still present get your vet to give her a course of flagyl. This is very bitter tasting so get the pills not the liquid and disguise it in some food. This will calm the intestines down.
3. Get her onto Royal Canin Prescription Diet Dry GI32. This is for runny bums, IBS, malabsortion, etc.
You can buy your Protexin, Panacur and Royal Canin GI32 from
www.hyperdrug.com
If all this fails it may be she will have to go on a course of steroids or go through food elimination trials if it turns out to be a food insensitivity. Also give her bottled water, not tap.
Good luck