I'm in middle of reading Harry Potter and the Deathly Hallows and I came across Lily's letter on page 180. Both she, and Harry in his reaction to the letter, mention Bathilda Bagshot. I assume her character was used earlier in the book or series. At the point of reading the letter, the reader is supposed to remember something about this character. I however have forgotten all about Ms. Bagshot.
I have a feeling Ms. Bagshot is important to the plot. (I feel she is important because Rowling tends to mention seemingly unimportant thoughts, ideas or characters only to use them for the basis of her plot later in her books). Though, as I am reading the Deathly Hallows for the first time, I am unsure as to the importance of Ms. Bagshot. This makes me reluctant to look her up, as reading an article on her character might include spoilers. I therefore ask the following question:
Without explicitly spoiling the rest of The Deathly Hallows, what is the reader supposed to remember about Bathilda Bagshot while reading Lily's letter? (Rowling also tends to quote obscure lines from previous books in the series which she is expecting the reader not to remember. She then proceeds to use that line as the basis of her plot. Please only mention what the reader is supposed to remember).