In honor of Rachel's 12th birthday (her adventure starts in September of 2023, so she is twelve today), here is a list of the other places stories about Rachel and/or her friends appear:

A story about Rachel and Sigfried:

FantasticSchools, Vol. 1 — Includes "Rachel Griffin and the Missing Laundry" — a Rachel and Sigfried (and Lucky!) story
Have you ever wanted to go to magic school? To cast spells and brew potions and fly on broomsticks and—perhaps—battle threats both common and supernatural? Come with us into worlds of magic, where students become magicians and teachers do everything in their power to ensure the kids survive long enough to graduate. Welcome to … Fantastic Schools.
Follow a mundane teacher striding into a world of magic, a spy on a mission, a guided tour of a magical school, a school dance for monsters, a dangerous reunion … and many more.
Follow us into worlds different, magical …
… And very human.
Stories by: J.F. Posthumus, Christine Amsden, James Pyles, Becky R. Jones, Morgon Newquist, Tom Anderson, Patrick Lauser, James Odell, Misha Burnett, Audrey Andrews, Christopher G. Nuttall, Paul A. Piatt, L. Jagi Lamplighter, David Breitenbeck

Gaius vs. the Giant Chicken!

Cracked: An Anthology of Eggsellent Chicken Stories — Includes "Frozen Chicken" — a tale of Gaius Valiant over Yule Break.
(This story takes place during Rachel's sophomore year, but there are not any spoilers.)
Chickens Land on Mars…
But what happens when authors have too much free time on their hands?
A challenge.
Craft a story featuring our favorite feathered raptors: the CHICKEN.
B'gawk!
Twenty authors deliver in some unexpected ways and live to crow about it.
From chickens in space to cozy murder mystery farm yards to schools of magickal thought…
Includes guardian angels, chicken shifters, aliens, and feathered matchmakers,
Maybe even a non-fiction adventure or two… and more!
These amazing chickens come from the minds of twenty cooped-up authors on the edge of cracking…
Read CRACKED: An Anthology of Eggsellent Chicken Stories.

Other stories in the Unexpected Enlightenment background:

Fantastic Middle Schools — includes "See You Down The Road" a story about the Roanoke Lower School.
Have you ever wanted to go to magic school? To cast spells and brew potions and fly on broomsticks and – perhaps – battle threats both common and supernatural? Come with us into worlds of magic, where students become magicians and teachers do everything in their power to ensure the kids survive long enough to graduate.
Welcome to … Fantastic Schools. In this set of stories, welcoming younger readers but still entertaining to all ages, we look at the lighter side of magic schools. Follow a young girl entering school for the first time – and another, desperate to go to a school that actually suits her. Watch a bully get her comeuppance and accompany young students as they go on a field trip, follow an expelled student trying to build a new life, and others learning the nature of magical creatures … … And many more.

God, Robot — Includes "The Ring of Sounding Brass" — Astrid Holywell's backstory, includes William Locke, Templeton Bridges, and Naomi Coils.
It is the year 6080 AD. Detective Theseus Hollywell has at last discovered the hiding place of William Locke, a notorious fugitive from justice who has been hunted for decades after committing unspeakable crimes.
But Locke has a trick up his sleeve, one that the detective couldn't expect: He has a story to tell.
This is the tale of the theobots, the robotic beings created to love God and neighbor with a perfection no human could achieve. In ten stories by eight different award-winning authors, Locke recounts the role of the theobots throughout history, from the purposes for which they were originally created to their ultimate role in deciding the fate of Man, the galaxy, and one lost and tortured soul.
(Note: only the part about Locke in the short story is canon.)

Planetary Anthology Series: Luna — includes "Merry by Gaslight" the backstory of Merry Vesper, only the ending is slightly different in the Unexpected Enlightenment version.
These are the tales of the orb that lights our night sky and drives the tides of our oceans. The bright companion that orbits our planet, invades our dreams and drives us mad.
The Curse and the Covenant by Ann Margaret Lewis – Tal, in the land of Ur, is son to a Lord. When a demon offers his father a gift to make him and his people like gods, Tal knows it’s a bad idea.
The Doom that Came to Necropolis, by Steve Johnson – Necropolis is a small town, complete with small town values and small town myths. Unbeknownst to them, their doom is about to arrive, riding a motorcycle, and armed with the weapons of science.
How to Train your Werewolf, by Margot St. Aubin – Jason Branch recently escaped from a home for the insane. His only goal now is to rest and be left alone in the woods. But when strangers decide that the same stretch of land would be perfect for their needs, they will soon discover Jason's true madness.

Tales of the Once and Future King — Includes "The Understudies of Camelot" — the backstory of a character Rachel will not meet for many years.
It is said that King Arthur will return in Britain's hour of greatest need. That time is coming. Four travelers, searching for the Pendragon, are quickly embroiled in a plot to rescue the beloved of a banished forest lord. And while they concoct their desperate plan a Bard, the new Taliesin, regales them with stories: Tales of Knights, yes, but also tales of robots and vampires, music and monsters, airships and armies – tales to inspire heroism and hope. And when all seems lost, perhaps these tales will be their salvation. This book is an anthology. This book is a novel. This book is a romance This book is science fiction This book is a fantasy This is "Tales of the Once and Future King"

After Punk: Steampowered Tales of the Afterlife — Includes "Hildy and the Steampowered Hounds of Hella" — the backstory of Hildy Winters.
While mankind can scarce hope to pierce the Veil without crossing it, a few intrepid souls will ever bend their will against the aether, combining artifice and the arcane to uncover its secrets. 
From voodoo death cults to the Day of the Dead, mummy parties, the wheel of reincarnation, the practice of death portraits, and so much more, these tales leave no gravestone unturned. 
Be it heaven or hell or the limbo in between, the hereafter is about to get 'Punked.
With stories by Jody Lynn Nye, David Sherman, Gail Z. Martin and Larry N. Martin, James Chambers, Michelle D. Sonnier, Jeffrey Lyman, Bernie Mojzes, Jeff Young, David Lee Summers, L. Jagi Lamplighter, and Danielle Ackley-McPhail.

Victorian Venus — Includes "Gaslight Jungle" — the backstory of Laurel Griffin's boyfriend, Charlie Fairweather
A future, one thousand years from now, where an echo of the Victorian past thrives on Venus. Terraformed Venus sees the culture of the era of high technology as one of innumerable dangers. Dominated by New Berlin, the most advanced society on the planet, the nation and city-states of Venus imitate both the technology and culture of the Victorian Era. As nations chafe under the yoke of New Berlin, war breaks out–driving a world so much like the past into a future entirely unlike our own.
This short-story anthology explores the regions and cultures of Victorian Venus, from the metropolis of New Berlin, to the tropics, to the Arctic Circle. The war between New Berlin and two rebelling nations forms the backdrop of most of the tales.

Mythic Orbits 2016 — Includes "The Last Flight of Odin’s Hundred" which is the backstory of a character at Roanoke whom Rachel knows by a different name.
Fourteen of the best speculative fiction stories by Christian authors, spinning science fiction, fantasy, horror, and paranormal genres into worlds of intrigue and delight.
Featuring Graxin by Kerry Nietz, author of Amish Vampires in Space and A Star Curiously Singing, Mythic Orbits 2016 has something for every speculative fiction fan.