Sticking to LTS releases was actually the worst way to do this as it meant catching 10.04 which was effectively a "one off" UI, resulting in two changes to the UI rather than one big overhaul.

My mother started off on 8.04 LTS. When upgrading to 10.04 LTS the window buttons changed sides and there was a new theme (this is enough to throw many users). When upgrading to 12.04 LTS there was a change from Gnome to Unity.

My mother now chooses to use a Mac because she was fed up with her computer "changing" each time I updated it. I doubt I could convince her to try any Linux distribution again - there are no perceivable benefits for her.