I think first thing is make it clear from your boss that who is in charge of the tasks/projects you are talking about. If it is your boss, and irrespective of you being a manager, you are just a team member like others, then you just have to do the best you can and follow her directions.
But if you are in charge, then as a team manager you need to take a firm stand on what is the right pace of the tasks and when to change direction or not. You can obviously take inputs from your boss but I think you should make it clear to the team and to your boss that any change in direction should come from you and not from her.
You can then have regular meetings with your boss either with the team or separately and update her on the activities. In either case, if she is "suggesting" a change, then you need to decide if you agree or disagree with her. If you disagree, then be prepared to push back gently or strongly or however it takes to maintain your ground. But I think your team can learn and grow if they see you take a stand as per your discretion (which I assume your team would agree with more) and fight back professionally if needed.
I used to have lot of heated discussion with my boss in front of my team (Though as a project leader and not a manager) whenever I disagreed with his suggestion. Because at the end I was responsible for the project and I knew best what was right. Of course it depends on your working relationship with your manager as well. We never carried any grudge and used to go along perfectly well immediately after those meetings!
Some of it is justified (the 'old' tasks are now no longer relevant), some of it, I think is a result of her stress (which is quite high and is justifiably so - it's a big, complex, many 0's job with constantly changing vision and needs)
I do not think you should make that correlation unless she confided in you. Just in case if she knows about your views on this, she may or may not appreciate you doubting her ability to handle stress! Whatever are the reasons behind it, you just have to think it as directions from your boss. You need to decide what would be your response to that.