Alexandra Manno was 16 when her boyfriend at the time gave her a surprise gift: a dog, which she named Calle.

A pit bull mix that appeared to have some Australian cattle dog in her bloodline, Calle slept with Ms. Manno every night, moving with her from North Carolina to the Seattle area, where she now works as a public defender.

“She’s been with me through college, law school, all my boyfriends,” said Ms. Manno, now 31.

In short, nobody in Ms. Manno’s life bore such intimate witness to her path to adulthood and self-sufficiency. So last year, when it became apparent that Calle was sick and needed to be put down, a tearful adieu at the veterinarian’s office wouldn’t quite cut it.

A friend of Ms. Manno’s told her about a pet funeral home in West Seattle called Resting Waters, opened in December 2016 in a low-slung brown building across from a popular deli by Joslin Roth, 39, and Darci Bernard, 34, who are sisters.