This poem describes a mother and daughter taking a walk into the field to see a newborn baby llama. It has rained and the ground is muddy and slippery. The further they go along on their journey, the more worried the daughter becomes because she is looking at her mother and realizing that the mother is getting older (she is 76, it says in the poem).
The family pet is running back and forth, and as the poem progresses, the daughter becomes more worried that the dog is going to knock the mother over or cause her to slip and fall. She says:
25. The black dog will not leave
26. though I shout No, bang him with my knee
27. when he jumps up. Our walk becomes
28. a journey, the dog,
29. the winter rains coming on.
The daughter is fearful in these lines -- so much so that she yells at the dog and kicks him. This event is a wakeup call for the daughter because she now realizes the combination of the dog, the winter rains, etc., pose a threat to her mother. So now, the walk becomes a journey on another level - a dangerous journey, whereas at the beginning of the poem, the daughter did not have all of these things to fear.
That's my view. Perhaps others will have additional insights.