But Williamson says her Hallmark Channel series, "Signed, Sealed, Delivered," will be just as comfortable a fit for viewers as "Angel" was during its 1994-2003 run.
"Signed, Sealed, Delivered," debuting 8 p.m. EDT Sunday, stars Eric Mabius ("Ugly Betty") as Oliver, the straight-laced, good-natured supervisor of an offbeat group of U.S. Postal Service employees who become sleuths to get mail to its proper place.
While mail carriers refuse to surrender to the weather, Oliver's crew is undeterred by a missing name or indecipherable address. In the first episode, a boy's urgent letter to an anonymous Grandmom leads them into unexpected territory.
Kristin Booth, Crystal Lowe and Geoff Gustafson co-star as the unlikely Sherlocks. Valerie Harper is a visiting manager in the first two episodes, with Carol Burnett, Valerie Bertinelli, Marilu Henner and former "Angel" star Della Reese also set to guest star.
The series is "a remarkably executed gem of a series, one that we hope returns the Sunday night tradition of families watching television together," said Michelle Vicary, the channel's executive vice president for programming.
"Touched by an Angel," a hit for CBS, kept within the boundaries of decorous storytelling. "Signed, Sealed, Delivered" does the same, with charms as old-school as the Post Office appears in an increasingly digital world.
There's gentle humor as well, which Williamson traces back to her TV roots writing for variety shows and sitcoms including "The Facts of Life."
On the flip side, Williamson said she hopes her new series will grow to encompass more complex and sensitive issues, such as "Touched by an Angel" did with domestic violence, human rights violations and more. Episode two of "Signed, Sealed, Delivered" about a PTSD-afflicted veteran, heads in that direction.
No matter the topic, the Hallmark Channel series will remain a "safe place" for families who still want and deserve less-edgy programming, she said.
"The television landscape has changed. But people don't change," Williamson said. She recalls seeing moms perusing the DVD shelves at her local store, "looking desperately for something they could watch comfortably with their families."
It was her own brood that kept Williamson away from TV: After "Angel" ended, she concentrated on raising her two daughters, now 14 and 12, with her husband in the Los Angeles area.
Inspiration for her return to series TV came in the form of a rediscovered box of "Touched by an Angel" fan letters that had gone unread. In a sense, she said, "they arrived right on time, just when I wanted to read them."
She was struck anew by the power of scribbled words and what they add to life and history: President Barack Obama's emails won't provide the insights that can be gleaned from a handwritten missive from 20th-century leaders like John F. Kennedy and Richard Nixon, she said.
Besides, Williamson suggests, in these days of hackers and snoops, "the most private thing you can do is send a letter."