Hey.
I honestly don't know whether this would be a good idea, or a bad one, but that's up to you;
What if... what if... you talked about your gf about a professional photographer? I know it could sound way more daunting to someone with body dysmorphia, but also, sometimes photographers are really good at handling shy subjects and being extra good at making people's comfortable. And to do it, she could take a bit of Dutch Courage or something idk an anti-anxiety pill, perhaps.
The point being that professional photos might make her see her body as more sexy as she usually looks at it in a mirror and not through professional photography.
Also it would mean you'd be able to make larger and larger prints as your vision degenerates. And even if she didn't want to look at them, or feel like getting naked at some point, maybe she'd still subconsciously realise that you really do think she's beautiful as you keep going back to browse the photos and have a quick wank lol.
Anyways, just a thought.