My first reaction to this was to get angry. If there was such a simple solution, wouldn't she still be alive?

But, luckily, I hit Google first. https://edis.ifas.ufl.edu/publication/FS437 showed that selenium does protect against mercury. Even dimethylmercury. And https://www.webmd.com/diet/health-benefits-brazil-nuts shows that Brazil nuts are an excellent way to get selenium. In fact it is comparable to a supplement, and a sustained diet of 3 nuts per day is already in the toxic range. I had no idea.

So it appears to be correct, there's a good chance that eating Brazil nuts could have saved her life!