Juana wakes before Kino because it is her duty to take care of the household.
Juana is a good wife and a good mother. She takes these responsibilities seriously. The tribe’s division of labor is very old-fashioned. It is Juana’s job to get breakfast ready and take care of the baby. Thus it makes sense that she will wake before Kino.
Juana's eyes were open too. Kino could never remember seeing them closed when he awakened. Her dark eyes made little reflected stars. She was looking at him as she was always looking at him when he awakened. (Ch. 1)
Kino values this in her. He considers her a good mother because she goes through the morning routine, quietly, day in and day out. Kino is the man of the house, so he does not share the responsibilities with her. He doesn’t tend to the baby or get breakfast. That is women’s work.
Behind him Juana's fire leaped into flame and threw spears of light through the chinks of the brush-house wall and threw a wavering square of light out the door. A late moth blustered in to find the fire. The Song of the Family came now from behind Kino. (Ch. 1)
To Kino, these little domestic moments are an expression of love. He loves Juana, and Juana shows her love by taking care of them. He loves this about her. He appreciates that he can depend on her every single day.
Juana is a strong woman. We see this later in her actions and words. She is the one who treats the scorpion bite, and who leads her husband’s decisions in what to do about the pearl. To Juana, taking care of her family means more than making breakfast. It means looking out for them and protecting them no matter what.