Best wishes for your mom's speedy recovery. I would definitely talk with Ortho about flying. I'm a PT and I've had patients fly not long after an injury like that, BUT there's a lot of factors that go into it. As far as the cruise goes, I hope that she is healed enough to go and enjoy it. I second the ideas of a scooter and asking about a handicap room. I know some of the rooms have a little step up to get to the bathroom so that would be a consideration if she can manage that. If she goes I would definitely see if she can get a chair for the shower. If she's getting PT right now I would definitely have her ask them to help problem solve some of these logistics with her.
