Lots of things can be responsible for Congestive Heart Failure. If she's up there over 65, then coronary artery disease, high blood pressure, diabetes, excessive drinking, thyroid problems, etc. can all cause it. Even old folks who get ill, have a fever where the virus attacks whole body and leaves heart, lungs in tired shape can keel over from congestive heart failure. Simply, the heart ain't pumping enough and that allows a whole host of problems to emerge like fluid build-up in the lungs, or in extremities (leading to edema) and this can tax the kidneys which try to help the heart pump by retaining even more fluid, etc. Seeing obese folks who wheez doing any kind of exertion is a bad sign and make them prime candidates for CHF.
Recovery isn't always a sure thing. The causes that led to down to the path of CHF need to be corrected. If that was bad diet, poor weight management, and lack of exercise, then suffering from CHF makes it doubly hard because with a heart that might give out at any time, how does one lose weight and exercise? The heart isn't working sufficiently to barely allow survival. And it's likely that poor diet and sedentary lifestyle caused this and those are brutally hard to change.
If the cause was partial liver failure, kidney failure, leading to CHF, due to say, excessive drinking, then it may be possible to stop, go through detox, and if you survive that, given time, the liver and kidneys might recover and then whatever blood diseases were spawned by bad liver and kidney function might reverse and then the heart recovers.
Typically, my doctors sent me to a seminar on staying healthy, and it was like a "scared straight" dose of reality. They told us in the room that once you get to the point of CHF, recovery is really hard. Once your system disables you that much, it's hard to survive let alone practice good diet and exercise. So mostly, they watch patients get ever more hospitalization, and one day, they die. It's best to not wait until you get CHF and really maintain health, take prescribed meds, and do the right thing.