It's no mistake that Mrs. Rachel Lynde's the first character we are introduced to. Mrs. Lynde is the town busybody. She knows everyone's business and tries to run everyone's life. You might think she sounds terrible (and she does have a tendency to make Anne and Marilla want to do the opposite of what she suggests).
But Mrs. Lynde isn't terrible. She's kind of funny, and sometimes, she's right. Her heart is in the right place, and a bit like Anne, she's very open, so no one ever thinks she's hiding anything.
Avonlea's an area without a telephone, so Mrs. Lynde kind of serves that role, spreading news back and forth between townsfolk. She's the person who tells Anne that she's ruined the Barry family's relationship with Aunt Josephine, and later, that Gilbert gave up the Avonlea school so Anne could have it. We can see how it might be useful for an author to keep a character like Mrs. Lynde around.