Well, I know there are snake traps available. They’re like glue traps, but not lethal. Once the snake is stuck to the trap, you can remove it with some oil and relocate the snake. I’ve not used them, but I did look them up once when my kids were wanting to catch a snake. My daughter then decided she was the Crocodile Hunter and now just catches snakes with her bare hands. You can’t really lure the snakes, just put the traps around and hope they slither onto them and get stuck. Poor little snakes.
Garter snakes, being harmless and beneficial, really should be left alone if your friend will consider it. We had quite a few snakes living around the deck area of our last house, and we never had a mouse problem. The snakes are much happier to be left alone, and if you get too close they will just slither away as quickly as they can.
@ChazMaz A garter snake bit my son when he was about two years old. It was a very big garter snake which my daughter had caught by the tail. My son toddled over, grabbed the snake in the middle, and then just stared as the snake wrapped around his leg and bit. He was so surprised and confused that he didn’t even cry. The teeth were like tiny little needles. We pried the snake off and called the doctor who said, “He’s fine. Just be glad you don’t live in Arizona.” I doubt my son actually remembers the incident, but he talks about it like it’s the proudest moment of his life. :)