GMAT Sentence Correction (SC) | Re: Emily Dickenson's letters to Susan Huntington Dickinson

Hi! I'm having a bit of difficulty in distinguishing between the different uses of "which" in sentence correction. I was under the impression that "which" had to directly refer to the the noun preceeding the comma e.g. ..the house, which was quite large, had many windows. However, in the example in my post this is not the case. Can you help?!! Many thanks!