Honestly, as much as Garth isn't someone Sam would work with, there are good reasons to put Allison in touch with him. First, Garth is part of an existing werewolf community. Secondly, he was a former hunter. He was something of a rare fit to the world Allison knew before. Dean does sort of fall as the fun uncle type. But Jack still sees him as one of three parents. He never would have learned to drive if not for Dean. Sam had helped him understand his powers better and that the world runs on social norms. Castiel provides him guidance above all us when it comes to Heaven. Unfortunately, there's some truth to parents never returning home without angelic interference. Jack would be a safer bet for questions as he has less tragic history in his life. "It's no fault of yours. You've helped me realize there are some matters I need to resolve. thank you."

There seems to be a lot of common ground between them. Cas feels this way about the Winchesters. "It's all right to feel as if you have two homes... It's what you do with the time you have while you are here." He is trying to make her feel better by having to wait to return to Heaven again.