Could be both, but if it was only about the clouds or the outside, Mrs Grieve's house (btw, what a suggestive name) would seem similarly dark.
You know the characters better, so you can probably tell if there's some sadness in Mrs X life, and if this darkness is metaphoric.
The cat might be a hint! Stereotypically, it's a must-have for every sad lonely spinster.
Student or Learner