Okay, I looked up the Redmond product. From what I understand, it's just salt? With maybe a few cents of trace elements thrown in? That the one?
Any type of mineral supplement that lists salt as the first ingredient is almost always not worth its salt
. The first ingredient should be some form of calcium (and not a crap source like limestone). All the milk production needs vast amounts of calcium. IIRC, something like .3% of dry intake (DM) per the latest NRC guidance. Phosphorus should be close, something like .2%. Almost to the 2:1 ratio for Ca:P. Good mineral mixes will have chelates not from EDTA, good forms of copper, like from copper oxide, etc. I would start with that and free feed a good loose mix. And if she's not having that, topdress the grain. Look for a horse or livestock mineral or even a goat mineral if there are no good ones at the store. Where do you go for the supplements? Out to the TSC in Ukiah?
Beyond that, your hay and pasture are the foundations of the milk. But your other cow is milking OK, so overall I think you're fighting all the previous malnutrition. Lactation puts so much stress on a cow, you need to make sure that the backbone (Ca, P, other macro elementals) as well as the trace elements are bioavailable.