My 10-year-old daughter is in my wedding as a junior bridesmaid, but I was wondering if there is such a thing as a junior maid of honor. My sister is my maid of honor.
A young girl in the role of honor attendant would be called a maiden of honor, and you can absolutely give your daughter that title while your sister remains maid of honor. It's just like having two maids of honor, or a matron and maid of honor.
Choosing Wedding Attendants
Basics for Bridesmaids
Your Bridal Party