I'm Aspie-ish, too, FWIW. I hated having my photo taken as a teen. Mum recently made me a scrapbook (for my 21st... in fact, that was two years ago and it's still not completed!) and there are hardly any photos of me between about 12 and 18. Do I mind? Yes and no. If I could have those pages filled with laughing, candid shots in which I looked semi-decent and was engaged in a variety of activities which represented me... that'd be fabulous. But the few photos I do
have aren't like that. They're horribly unattractive - not just the kind of photos that are unattractive at the time but look OK a few years later, but the kind that still make you wince ten years down the track. Horrible. I have a horrible bushy fringe, bad skin, bad glasses (in some pics), and a variety of expressions ranging from the dimwitted to the manic. They do not bring me joy. They make me go "eugh". Would my life be enriched if my mother had forced me to pose for dozens more of the horrible things? No. I wouldn't have minded if she'd taken the odd candid photo and deleted it if I looked silly in it; but she never seemed to think of that.
I still can't smile naturally in photos (or in any situation, really!). Luckily with the advent of digital cameras and my family becoming more photo-savvy, we have the odd candid shot in which I look OK. But I still hate being forced into photos against my will, because I know the chances are very high that I'll look stupid
- not ugly necessarily, just ridiculous, with a weird twisted mouth or half-closed eyes. Who wants that?
I vote "she'll probably grow out of it, but whether or no, it's her body and her business". That doesn't mean you can't try for a compromise - say, an arty shot of her standing in an archway from behind, so you just see her hair and the shape of her coat, or a sepia photo of just her eyes peering over a book, or something similarly quirky. If she feels "safe" being photographed with sunglasses, so be it; just having her hands photographed, so be it; taking her own photos, alone, with a timer; or whatever. If not, please don't force her. It's her image, and her body, and her embarrassment. If grandparents are an issue, can't she write them a letter or something instead?