Mrs. May is a nice lady who lives in Kate's parents' house in London. Oh, and she's Kate's best bud. She teaches Kate how to crochet and first tells her the story of the borrowers.
Mrs. May is a good influence on Kate. While others call her "a wild, untidy, self-willed little girl who stared with angry eyes and was said to crunch her teeth" (1.1), we learn that she is not this way with Mrs. May: "Kate was never 'wild' with Mrs. May, nor untidy, nor self-willed; and Mrs. May taught her many things besides crochet: how to wind wool into an egg shaped ball" (1.3).
Mrs. May "gets" Kate in a way that others do not, so it's no wonder they like to hang out together and crochet. And it's a good thing that Mrs. May and Kate get along so swimmingly together, because they become the narrators of our story, and when the facts stop, they together imagine the ending. Without our dynamic duo to tie up loose ends, we would totally be left hanging.
There is a certain loneliness about Mrs. May. She doesn't seem to have a family of her own, and the narrator herself is not even sure why she lives in Kate's parents' house: "she was, I think, some kind of relation" (1.2). Um. So what's she doing here, then?
All we really know is that she lives in "the breakfast room," which is a nice room in the morning, but kind of forgotten about later in the day:
Now breakfast-rooms are all right in the morning when the sun streams in on the toast and marmalade, but by afternoon they seem to vanish a little and to fill with a strange silvery light, their own twilight; there is a kind of sadness in them then, but as a child it was a sadness that Kate liked. She would creep into Mrs. May just before teatime and Mrs. May would teach her to crochet. (1.2)
Perhaps Mrs. May is like her morning room—a nice lady, but in old age kind of left on her own. Maybe that's why Kate goes to keep her company, and learns the story of the borrowers.
Here's your daily dose of sad: Mrs. May's little brother died many years ago on the North-West frontier. It was he who first told her the story of the borrowers, and Mrs. May wants to remember and believe the story as much as she wants to remember the memory of her brother.
"I do remember, […] Oddly enough I remember it better than many real things which have happened. Perhaps it was a real thing. I just don't know. You see, on the way back to India my brother and I had to share a cabin—my sister used to sleep with our governess—and, on those very hot nights, often we couldn't sleep; and my brother would talk for hours and hours, going over old ground, repeating conversations, telling me details again and again—wondering how they were and what they were doing and—" (1.40)
Mrs. May herself gets caught up in the story, in the mystery and fantasy surrounding her childhood memories with her brother, and passes them on to her young friend, Kate. Which tells us that the story of the borrowers is a story for the young—those whose imaginations are still ripe and eager.