I was wondering why Henry would need to 'babysit' his sister, so to speak if she stayed at his home. He could still live his lifestyle the same as ever while Mary oversaw the daily needs of the household. She could hire a companion if need be and have friends rotate in and out on visits and giving return visits to London. If Henry was showing brotherly concern, he would have been happy to help her out instead of leaving her to work something out for herself.