Somehow this doesn't make sense to me

Wouldn't the snake bite her when Lexi jumped on it, and I always thought Garter snakes are harmless and don't "attack" if they are not provoked (from what I know, but then again I am no expert.) so I find it hard to believe it jumped at your ankle? Also, if it was that riled up and was going for your ankle then I don't think a dog would make it just slither away?