It could be a lot of things,but the first thing that comes to mind is that his intestines have gotten twisted.This happens a lot in larger breeds.Especially the "wasp-waisted" ones,like Wiemeraners,Great Danes,etc.It's called intestinal torsion.A lot of vets don't think to check for it,they'll test for parvo first,because the symptoms are similar.Loss of appetite,sometimes diarrhea,dehydration.Surgery is required,and if it isnt done,they go down fast.

It could also be that he's swallowed something and caused a blockage,but I doubt she would have two dogs do that at the same age.It could also be parvo.But I would have the vet check for torsion right away.

I hope she gets it resolved.Weimeraners are great dogs,one of my favorite breeds.Give her my best.Love ya.