90, WOW!! So many "it depends on...." to consider: her health, her state of mind, her ability to keep up with an 11 yr old. Heaven forbid, if something should happen to Grandma overseas, who would provide medical info necessary to give her proper care. The child would be complete freaked. Children have a way of blaming themselves in situations like this. Even if Grandma's in great health - she is 90 and our parts aren't designed to last forever. You mentioned this is a tour group, they are probably wonderful people, but my child is not their responsibility. Regardless of my feelings for Grandma, I just couldn't allow it and Grandma, Hubby, the child and everyone else would just have to deal with it.