A bright little girl probably has many excellent papers. Display them prominently on the refrigerator. Have her put them in letters to grandparents and other fond relatives. After school each day, look over your daughter's work with her and show a genuine interest in what she is doing at school. She needs to know that you value how well she is doing.
Make it a point to avoid comparing your children's skills in reading, math, and other areas. It can only lead to feelings of inferiority in one child, as well as sibling rivalry.
Please keep in mind that kindergarten teachers don't consider parental help in developing reading and math skills as important as developing language, thinking, social, self-help, fine motor, and speaking skills in preparation for school? Most of your son's time should be spent in learning about the world from the hands-on experiences he will get through play.
As you have said, your daughter should not be expected to be reading independently. Kindergarten children, typically, only start reading toward the end of the year. For now, focus on increasing her motivation to read, not on actually having her read. The best way to do this is by reading to her as often as you can.