I think there are some models that are "less than user friendly" -
For example, from what I have read the first "new" Bernina 830s - very expensive machines - were not user friendly - and temperamental.
An understandable user's manual/guide is important.
Also , will the machine require attending classes to learn how to use it? And if so, are they available and will granddaughter be able to get to them?
You might have using your machine be a special treat for when she visits you.