Pipes freezing in an apartment in Paris? That is what sounds highly improbable.

And about the windows, well she probably shut the windows when she left (not sure how it's called in English actually? closing the wooden things that cover the windows).

Accidents do happen, but an unoccupied apartment that has not had a water problem or a broken window in 70 years? I don't see a problem, especially in such a non-hostile environment.