My 5 year old just had very green mucus on/in her stool. complains often of stomach aches. what should i be worried about?

Mucous is unusual: Regardless of the color, mucous in stool can be a sign of infection or inflammation in the intestines. If the stools are loose or watery, this is even more likely. I would recommend that she see her doctor and that a stool test be done to check for a bacterial/parasitic infection or malabsorption of fats and proteins. Tests can take 3-5 days to obtain results.