My DS was about 10 when we told him...but he wasn't diagnosed until he was 13, so it had to be - the Dr thinks you might have etc. etc. which made it trickier.
We knew from age 7 that he would eventually be diagnosed with something, but they kept reassessing to decide exactly what to diagnose him with, that was why he was so old when we told him, I was trying to wait for a firm diagnosis. Eventually though it got to the point that he was so unhappy with himself that I felt I had to tell him something.
I told him that we and the Dr thought he has AS, told him that it meant his brain was wired a bit differently so that was why he was struggling to learn things that other children just know, why his handwriting was so bad - that he was normal, for someone with AS and left it to sink in a bit.
I then got him everything I could by children with AS and took him to groups for children with similar diagnoses (is that the plural? Lol).
He's now 16 and much much happier in his own skin, in fact he was busy telling me the other day that the world would be a much better place if everyone was autistic, quieter, more logical and apparently we'd have perfected cloning and space travel
lol.
I don't know what there is out there information wise for NvLD, but could you introduce her diagnosis to her, then give her AS stuff and tell her they're similar...DS knows about autism, AS, ADHD, how they overlap and when reading things about AS knows that some of the things described don't apply to him as no two people are affected quite the same way anyway - if you're struggling to find suitable specific things it might be an idea.