Not a problem from a single joist. But if it will make her feel any better and that's important to you, you can run a doubled up two by four between two joists. This will spread the weight across two joists and may ease her mind. As far as the pulley system, it seems a bit elaborate. If you hang a rope from the joists low enough to reach the top of the bag, you should be able to grab the bag with both arms in a hug, lift it up to take the weight off the hook while supporting the bag with a leg, your chest, or stomach and reach up to unhook it or rehook it. It would also help to build up those arms.
