Hello and welcome to HealingWell. I will try to give you some info re A-fib.
First of all after your aunt's first cardioversion was she sent home on coumadin ( warfarin)? Most people need to take warfarin for at least four to six weeks after cardioversion to prevent a blood clot from forming even after your heart is back in normal rhythm. Warfarin prevents formation of blood clots and can reduce ongoing clots.
Sometimes atrial fibrillation can't be converted to a normal heart rhythm. Then the goal is to slow the heart rate to between 60 and 100 beats a minute (rate control). As you mentioned (AV) node ablation is sometimes the answer as well as medications.
I would really encourage your Aunt to make a list of questions she has for her Dr. and make sure she gets all the answers in layman's terms.
It is so good to see you caring for your Aunt as well as advocating for her.