You're going to be fighting it until your pastures come back in. There is a dietary reason that you've been dealing with it now. Green grass and freshly cut hay is loaded with Vit A. As hay ages, the Vit A content declines dramatically. When the pastures go dormant, the Vit A is nonexistant. The horse will store Vit A in the liver and draw on it throughout the winter. When the level is low, you start to see deficiencies such as RR and goopy eyes. Most of your RR will start around the first of the year for this reason.
The simply solution is to add some VitA to the diet. Go buy one tub of Mare Plus (or a similar supplement you want at least 1,000,000 IU/Kg). Hoffman's makes a nice product. Double up the portion for each horse until it's gone. Try for about 100,000 IU/day. Problem should be done. Even if you're feeding a fortified concentrate, the older mare isn't going to be as efficient with her food so she needs extra.
Next winter, get both of them on the Hoffman's or other product by the end of September. I would actually have both of them on it year round.