Hi Lamilu,
As far as I understand MDS is a more severe diagnose than AA. Patients with AA can be cured with drugs and only few patients with the type of MDS that is on the border to AA perhaps can be cured with drugs.
Then I have understood from other members that neutropenia in AA patients isn't as dangerous as neutropenia in MDS patients. I still think 0.4 is very low but your mother doesn't need antibiotics now.
AA and MDS are both bone marrow diseases and your mother's doctor should know much about both diseases if she is a specialist in MDS.
In any case you could look at these advices for patients with neutropenia. It is old but all the neutropenia sites look the same to me. I live like I have neutropenia since I had neutropenic fever Sept 2007 and have not had any infections (knock on wood).
http://www.neutropenia.ca/about/living.html
Heart fibrillation is quite common - your mother must have medication (like digitalis) for that symptom. Be sure that she is getting the best possible care for her heart.
Kind regards
Birgitta-A