What important lesson had the narrator learned by the start of the next spring?

By the start of the next spring, the narrator (Bright Morning) had learned that a good shepherd never leaves the sheep to fend for themselves.
In chapter 1, we learn that the narrator had left the sheep on the mesa the previous spring. She did so because she was afraid of a gathering storm.
The storm had begun innocently enough, with a little rain. Bright Morning remembers herding the sheep into an aspen grove. Her goal was to wait out the storm there. However, the rain soon turned into snow, and she began to fear. Eventually, Bright Morning left the sheep, resolving to return the next day for them.
When she returned, she was greeted by her sister (Lapana) and her mother. Bright Morning remembers that her mother had handed her a blanket then, put one on herself, and walked out the door. The two climbed the trail all the way to the mesa in the falling snow. That night, Bright Morning and her mother waited out the storm on the mesa with the sheep. Bright Morning remembers that it was a long night because her mother remained silent the entire time.
When the morning came, the two drove the sheep back down the trail, across the river, and into the brush corral. Bright Morning remembers that her mother didn't even speak to her then.
Bright Morning relates that her mother has never spoken of that night again. Additionally, her mother didn't allow her to take the sheep up to the mesa for the rest of the spring. Bright Morning remembers that someone else took the sheep up to the mesa in the summer and fall.
So, now that a new spring is here, Bright Morning hopes that her mother will again trust her with the sheep.
The text tells us that she needn't have worried. Her mother is waiting at the gate of the corral when Bright Morning returns from the river. She tells Bright Morning to take the sheep to the south, beyond the aspen grove.