I do recall reading something similar once, but I tend to take everything with a grain of salt, so to speak. There are lots of experts in the world, and if we listened to all of them we would live our whole lives in fear!
I have 1 RIR girl (out of 6 in total) who lays a double-yolker fairly regularly. It is not so much the 'double yolk' part that worries me, more the fact that the double yolks come wrapped in massive eggs, the largest being 118 grams! Obviously it is not
ideal for our girls to be laying eggs of this size, but that raises the question of what can we do to prevent it?
The best advice I can give you on the matter (and this stands for all chickens) is to keep a close eye on them. Make sure their diet is adequate, that they have good shelter and access to free ranging if possible, never let their water run dry, practise good hygiene in the coop and run, and take preventative measures such as worming and dusting for lice and mites, rather than corrective measures after the fact (if possible.)
That is the very best we can do for them, and after that it is in Nature's hands. What will be will be. My girl has been laying her massive eggs for about 9 months now. She seems fine. I do keep an eye on her and always check her back end for prolapse when I find the big eggs, but other than that I just try not to worry and trust that she knows what she is doing.
My very best wishes to you and your girl,
- Krista