Thanks for writing your query.
After reading your post, I would advise that you should get her clinically examined and investigated.
Black coloured stool means that there is bleeding in the gastrointestinal tract.
I would suggest following investigations :-
2. CT abdomen.
3. Complete Blood Count(CBC).
She can take an antacid
40 mg along with Domperidone
Antacid in gel or liquid form is also beneficial as it forms a protective layer over the damaged mucosa.
Following precautions may be helpful :-
1. Avoid spicy and oily foods.
2. Do not remain empty stomach for long periods.
3. Avoid self medications, especially painkillers and steroids
4. Avoid smoking, alcohol, if any.
5. Drink lotsof water daily.
I hope this is helpful to you.