I would start her on 3 tablespoons in the AM (2 tbsp = 1/8 cup), and 2 tablespoons in the PM
I think 3/8 cup will be too much. She's old enough now to be on 2 meals a day, so this is a great time to make the adjustment. That is of the DRY mixture -- you rehydrate then with the same amount of water and let it sit, then stir up a bit before feeding, of course. It should have a stuffing-type consistency.
So...add (hot) water...1 tablespoon for each tablespoon of dry THK...stir...let sit 10 minutes...stir...feed
ALWAYS clean out bowl between feedings. Because it's essentially raw, it goes bad in the same way a raw chunk of chicken would