It will probably work better for her with as you have said 9-10 inches off. She'll look the same just a little lighter on the shoulders if you know what I mean. You can ask that the hair be donated to Locks of Love if you wish, they use the hair to make wigs for people who need them.
I think she would look adorable right at or below the shoulders.. That long would drive me nuts! Trust me, my mom never used to let me cut my hair and now I can't have it much further than my shoulders without it making me crazy.
She's adorable. This might sound selfish but I would look into selling it. Find some credible websites. You could make like 2-4 grand for "virgin hair". Put it towards a college fund for her or something.