Kelly Kenney was taking a late-night walk to clear her thoughts in her Los Angeles neighborhood this spring when a colorful pinwheel caught her eye. She stopped and found herself gazing down at an elaborate fairy garden at the base of a tree, complete with painted rocks and tiny trinkets.

Pinned to the tree was a Polaroid picture of the garden’s creator, a young girl named Eliana, and a poem using a medieval-looking storybook font that told her neighbors how to use the garden: “Our 4-year-old girl made this to brighten your day / Please add to the magic, but don’t take away / These days can be hard, but we’re in this together / So enjoy our fairy garden and some nicer weather.”

Ms. Kenney hatched a plan, and on the next night, she left a note at the garden pretending to be a fairy named Sapphire, after Ms. Kenney’s September birthstone, who had taken up residence in the tree. She promised she’d leave glittery magical resin dice (a pandemic hobby for Ms. Kenney) if Eliana completed three tasks she listed that were etched in kindness. And the next day, they were finished.

The note kindled a friendship tied to the fairy garden that would last through some of the darkest months of the pandemic and hardships of 2020 for both a little girl and her grown-up neighbor. Ms. Kenney chronicled the experience in a wildly popular Twitter thread this month.

“I felt like immediately when I found it, the whole family wedged themselves into my heart,” Ms. Kenney, a photographer, said about the fairy garden. “I was so alone at the time, physically and mentally, and I felt like these people were kindred spirits.”

Eliana made the fairy garden on April 28 using materials from her grandmother. The garden started with fairy-size doors on the tree, a couple of fairies and a gnome. It grew with contributions from neighbors, like a tiny purple vanity with a quotation from “The Lord of the Rings” inside, Eliana’s mother, Emily Pauls, said.

Ms. Kenney found a new purpose as she went through a harsh breakup by orchestrating elaborate notes and photoshopping herself as a tiny fairy next to her cat, Nova. She gave Eliana’s parents her phone number, to reassure them, when the letters became more frequent.

She pondered ideas for imaginative gift boxes to leave behind, with the goal of making each better than the last one. Ms. Kenney tapped into what she said she loved when she was a child and texted Ms. Pauls for help.

Ms. Kenney gave Eliana a stuffed pig and a goat; a pop-up version of one of her favorite childhood books, “The Little Prince”; and Crayola markers with paper so Eliana would stop draining her parents’s supply of copy paper when she draws.

As a child, Ms. Kenney said, she was bullied because of how her creative personality manifested itself. She felt ashamed, and it wasn’t until later in life, with her uncle’s support, that she tapped back into her imaginative side.

Noticing that she and Eliana had similar personalities, Ms. Kenney wanted to nurture Eliana’s creative inspiration and provide a positive influence, something she had lacked growing up.

Eliana’s parents found that she changed over the past nine months, too. Through Sapphire’s encouragement, she was becoming more imaginative and kind during a time when she needed a role model since the pandemic halted her year in preschool.

Ms. Kenney encouraged Eliana to write stories, which led to “Sapphire the Explorer.” It included illustrations and a song that only fairies can sing (and read). Ms. Pauls helped with punctuation and turning her text into pages.

Eliana often thought about Sapphire and wrote to her, asking what the skin of fairies felt like and what things Sapphire owned. Ms. Pauls said that Eliana would pick up items like a rock and think about how Sapphire could use it as a table or dreamed of ways to catch the fairy.

“She’d never seen me, but this relationship we have is definitely love,” Ms. Kenney said about Eliana. “She’s just as magical to me.”

Then the adventure encountered a plot twist. Ms. Pauls let Ms. Kenney know in mid-November that they had closed on a house in south Los Angeles and would be moving from the West Side, leaving the neighbors to tend to the fairy garden.

Ms. Pauls asked Ms. Kenney to help support Eliana, who was having difficulty coping with the move. Ms. Kenney told Eliana in a letter that she would also move — out of the garden to a bigger tree for Sapphire and her growing cat.

“Sometimes, we outgrow homes because we have too much love and need a place we can hold it all,” Ms. Kenney wrote. “But it is so fun to find new trees and imagine what new adventures are in store for us!”

Eliana’s mother and Ms. Kenney planned to meet as the family said goodbye to their neighborhood on Dec. 11. Ms. Kenney and Eliana’s parents were tested for the coronavirus days earlier in an effort to ensure the visit was safe. In another letter, Ms. Kenney hinted to Eliana that she would be coming to get her final things and that fairies grow to be human-sized when they are moving.

Dressed in character, with pointy fairy ears, Ms. Kenney walked up to the tree and, as she rummaged around the garden, pretended to look startled by Eliana. But Eliana was the one who was stunned and overcome with emotion. Ms. Kenney crouched down and they began to chat about Nova the cat and what life is like as a fairy.

“Every time, it was always this sweet, sweet moment where I felt so strangely known by the stranger,” Ms. Pauls said about the letters. “Through this whole exchange, she’s become family in a way. It’s a really unexpected way to find a friend.”

Ms. Kenney continues to bring the magic to Eliana through letters and video chats. But there is more to be found when Eliana makes another fairy garden at her new home, and hopefully, another fairy will move right in.