Some important causes of anemia like bleeding from the intestines, intrinsic factor deficiency, etc. have been eliminated.
I would suggest that you consult a hematologist
. A hematologist is a specialist in blood diseases.
Persistent anemia needs to be investigated further.
Other causes of anemia for which she needs investigation is to find out whether there is any bone marrow suppression. For this she would need a bone marrow aspiration.
Her type of hemoglobin also needs to be evaluated, with a full hemogram.
For all this, you should consult a hematologist. You should discuss about bone marrow aspiration with him.
Once the cause of the anemia is found, this cause can be treated.
There are many causes of anemia, icluding renal diseases, etc. All these need to be investigate for and ruled out.
You can look up here:http://www.emedicine.com/med/topic132.htm
I hope this answer was helpful. If you need more information, feel free to ask. For accepting this answer, please click on the green 'accept' button below. Feedback/Bonus will be warmly appreciated.