I can fully sympathise with your concern and understand where you are coming from. You don't state what actual treatment she received in Jan 2011, for her heart attack? Did she have stenting at that time?
Her EF has dropped quite a large amount in one month, and so there is obviously something going on, like a blockage in the coronary arteries. She is probably already on medication, so to leave it would likely see the condition get worse. 35% is borderline as being classed as CHF and you want improvements as soon as possible. An angiogram is the only sure way to see what is going on, and while in there, have any obvious large blockages intervened if possible using stents. I wouldn't leave it.
My case is same. If your mother do not have chest pain then it may be possible to manage her with medicine. I had two heart attacks. I am still managing myself with medicines only inspite of blocks in coronary artries to the extent of 90%.Life style changes too are necessary. You may go through my postings.