My most urgent suggestion is that she have her thyroid hormone levels checked immediately. I would hope this has been done but have seen obvious causes of tachycardia like this overlooked. Hyper thyroidism is very common, especially in females and can be a cause of tachycardia and a fib both. It is treatable. Her heart rate is extremely high and I can’t imagine any cardiologist taking a cavalier approach to her problem. Her primary care doctor can order, the thyroid hormone levels and you would have results within a day or two. If that hasn’t already been done. .