i believe that she has 'passed over'. the dream seems to be saying that
your nana is available to provide you with wisdom "from the other side".
you have made preliminary contact, by removing some snow from her
window, to inform her of your presence. when you look through that
window later, you see that a thaw is underway. although she was 'upstairs'
(in a higher realm) in the dream, communication was initiated.