Bridesmaid Dilemma

I have always dreamt of having my two best friends , who are the same age as me, as my bridesmaids.  I also plan to ask my partner’s little sister, who is under 10. My sister, who is much older than I am, has hinted that her dress had better be a decent one… My sister and I aren’t that close, but I was her bridesmaid over ten years ago. Should I ask her? I do not want to hurt her feelings.