I recently found on my overflowing bookshelf a marvelous little biography entitled Road to Siena: The Essential Biography of St. Catherine. I didn't know this until I started out, but it was originally published by Edmund Garrett Gardner in 1907. Fortunately for modern readers, Jon M. Sweeney came along and edited it, rendering sentences and wording to fit the current age. It's an easy, informative read. And if that doesn't convince you, Evelyn Underhill, the great compiler of mystical writings and thought, referred to Gardner's biography of Catherine of Siena as "the best modern biography." That's high praise.
What I liked about this book is that it presents both the historical context of her life as well as personal details without intruding by offering unfounded psychological analyses. I'm sure you've read books where the biographer tries to make a point about someone's psychological makeup that after a while feels tawdry or even gossipy. You won't find that here. It's well written, well-paced, and presents a woman in all her complexities in an age very different (and in some ways very much the same) as our own.
Catherine of Siena knew early on that she was destined to work for her Lord, and she did so to the best of her ability. She lived during a perilous, rocky time when governments were unstable and religious institutions racked by hypocrisy, scandal, and division. She spoke her truth to power and worked for peace and stability. She died at the age of thirty-three, having left behind 380 letters, twenty-six prayers, and her Dialogues, which some have compared to Dante's style. This mystic deserves your attention.