Most dairy rations are 16% protein. If that is what you are using, it could be something else. If you are tether the Tog and only started recently, perhaps she is not getting the browse she needs to maintain milk production. Since she's a purebred, her nutritional requirements could be higher than the mixed breed goat you lost. This could mean she needs "better" hay, higher protein feed, etc. Check the website....lots of the cow owners there have goats too.
For me, I switched from feeding corn/oats/barley to a mix that included grains with alfalfa, wheat mids (higher in protein) and a little soy (which I prefer to avoid but haven't had the time to eliminate).
Good luck!
Kristin