My DD had her first period during the weeks they had swimming for PE, so "started out" with them. Since then, she went through a time where she exclusively used pads - but is now back to using tampons.
I think the instructions included in the boxes are excellent ... just let your DD know that she can ask if she has any questions about the instructions and that it may take a few tries to get it right ... that once she figures it out, it will be easy.
In your particular case, I think making them available (the smaller the better is great advice) is all you can do. When she's got enough motivation, she'll attempt it on her own.
p.s. We went through a similar thing with my son and contact lenses (both my DH and I wear them). He wanted them very badly at age 9, but got REAL frustrated trying to put them in (screaming, crying, etc). I just told him that it was HIS choice, even though we had purchased them he didn't have to wear them. Well he wanted to BAD ENOUGH that he just stuck with it and after a week had the technique down.