Hope you don't mind me joining in. I suppose everyone feels differently about family trees. But to me it is a tribute in a way to every person on my tree. They are not rich or famous, none of them would be remembered, so I feel responsible for every person I add, and feel they have a right to be remembered, no matter how ordinary they were.
I feel through my research it gives each of them their place back, for example my Grans two little sisters, they died within 6 days of each other aged 1yr and 3yrs, and none of us knew they had ever lived untill I started my tree, my Dad and his cousin aged 93yrs were so moved when I told them of the baby Aunts they knew nothing about.
The soldiers from WW1 and WW2. My Mother had a young Uncle who died before she was born, I told her and her siblings about him, and managed to find a picture. I also found a picture of Mums Dad who got a DCM and she cried to see him so young. Least we forget? Yes they would be forgotten if not for the tree.
All of these things are out there to be found, if I can, anyone can, so little is private.
But as long as the living are safe guarded and nothing bad is on a tree, then I feel they should be seen as memorials to those gone before.
I hope one day your sister comes round and even shows an interest, but if not don't mention your tree, and see yourself as the guardian of each person who lives on in its' branches and you wont go far wrong, good luck XX
