Hi brightspark, it is such a hard situation for your DD. I sh significantly from age 15 to 23, and, whilst I am pretty much over it, still have the intermittent relapse - these have been triggered by major events such as exH leaving me and my babies, my dad dying suddenly.
I used to very rarely go without long sleeves and feel genuinely sad that my wardrobe is so limited. My scars on my legs have faded considerable, as have those on my chest, but my arms never really faded - I also have keloidal scarring. Surgery was never an option for me as my arms are completely covered from wrist to shoulder. Again, make up is of limited use when scars are keloidal.
What I did, about 18 months ago, after years of fretting, was start work on having my arms tattooed. Sounds a bit weird, but I have always liked tattoos, and had a few anyway. I came to the conclusion that I wanted to be proud of my body, and so I designed a really beautiful full sleeve tattoo for my right arm, which is pretty much finished now. It took a while due to finances, but the tattoo artist who worked on it was so careful about covering the scars. It isn't a standard tattoo at all - very feminine despite being all black. Anyway, I know that tattoos aren't for everyone, but I work in a senior management position and also teach. I wear long sleeves for work to cover the tattoos, but on nights out and days off, I can, once again, wear short sleeves. To me, it feels more socially acceptable to have tattoos than to have obvious sh scars.
Half of my left arm is now covered, and hopefully end of next year I will have the lower part finished.
Anyway, this was my way of beginning to make peace with my scarred body. I have to admit that the past month or so has been tough, and my untattooed lower left arm has been attacked a little. But only very minor injuries, and I haven't touched my right arm at all - so the tattoo has helped in more ways than one. I think that it will take time for your DD - as others have said, it really does take time for the scars to fade, but once that happens, it is possible to find a way to accept your body.